How do people who believe in immediate heaven for believers at death explain Tabitha?

Conservative Protestants typically use the phrase "intermediate state" when talking theologically about the "immediately-in-heaven" view.  Wayne Grudem is a conservative Protestant representative of this view.  In his book, Bible Doctrine, on page 352, Grudem writes,

"The souls of believers go immediately into God's presence.  Death is a temporary cessation of bodily life and a separation of the soul from the body.  Once a believer has died, though his physical body remains on earth and is buried, at the moment of death his soul (or spirit) goes immediately into the presence of God with rejoicing."

Grudem mentions 2 Corinthians 5:8, Philippians 1:23, and Luke 23:43 in support of this view.  However, he offers no suggestion of exactly what is happening in the case of a miracle when a person is raised from the dead.

From the theologically conservative Protestant position, Tabitha and others like her pose no problem, because the view does not necessarily state that once a believer dies, that person... never returns to life again.  Rather, that is the normal occurrence for both believers and non-believers.  But, God may choose according to His pleasure and mercy, to allow the miraculous to intrude into the ordinary and raise/resuscitate a dead person, again whether believer or non-believer.  That's what makes it a miracle, whether the human agent is Peter praying or a doctor reviving the one who is clinically dead.  Note that this is not merely relying on a miracle to get out of a theological issue.  Rather, the question assumes that miracles do occur.

For the person so raised, what has been his or her experience?  Alas, the Bible is silent on that question.  We do know that the unmerciful rich man suffered apparently as soon as he died (Luke 16:19-31) and returning was denied him.  The Apostle Paul may have actually died in Acts 14:19 and some have speculated that may have been the experience he refers to in 2 Corinthians 12:1-4. Admittedly, that connection is speculative, but if so then Paul experienced the intermediate state and returned.

When reading of an after-death-return-to-life experience, it's best not to put too much stock in it, but whether believer or unbeliever, there is nothing about the intermediate state that prevents a miraculous return to life after dying.


Is there a special name for the day between Easter and Good Friday?

Liturgy Brisbane calls it "Holy Saturday."
According to the Catholic Encyclopedia, it is a day of both joy and sadness, and "in the early Church this was the only Saturday on which fasting was permitted, and the fast was one of special severity. Dating from the time of St. Irenaeus, an absolute fast from every kind of food was observed for the forty hours preceding the feast of Easter."
The names for the full week:

Passion Sunday (Palm Sunday)
Monday of Holy Week
Tuesday of Holy Week
Wednesday of Holy Week
Thursday of Holy Week (also called Maundy Thursday in reference to Jesus' command to wash each other's feet)
Good Friday
Holy Saturday

The days following Easter Sunday are called Easter Monday, Easter Tuesday and so on through to Easter Saturday, which is 6 days after Easter Sunday
The Sundays of the Easter Season are named the Second Sunday of Easter, etc, not after Easter as in the past, because they fall with in the 50-day Season of Easter.
(Liturgy Brisbane)


When was the actual Transfiguration of Christ?

The actual Transfiguration according to this source took place in February or March: -

  Though the Transfiguration took place in February or March, it has
  always been celebrated later in the year.


What is the theological basis for readmitting a Protestant preacher to preaching after divorce?

I hope the following does indeed contribute to the answer....

Paul writes that an elder must be above reproach, blameless, the husband of one wife, manage his own family well etc from 1 Timothy 3 and Titus.
A divorce is seen as causing serious question marks on these things for the man who has gone through such a tragedy.

Since the qualifications from Paul are not "ought to haves" but "must haves", then it has been the case in many Protestant denominations, that a divorce will disqualify a man from continuing to hold public office in the church.

It in no way condemns the divorced people to not being christians any more, if there is repentance, but it does preclude a man from continuing in the office even if he is the innocent party.

That's how it works in the circles I have seen....

But for those circles that do allow Pastors to re-enter the teaching office, it is generally because of arguments like "Who are we to judge? If a man is innocent then it should not disqualify him. If he has repented then we should bring him back and welcome him as a brother."

Such reasoning though is contra the first set of principles.


There is one God who has revealed himself in three persons.

The vast majority of Christians across all major sects agree that Jesus is both the Son of God and God. This has been articulated many mays, but is not easy to explain in the confines of language. He is not the "son" as is a physical offspring as the result of sexual relations, but in another sense of being "begotten". Not created (as he always existed), and not lesser than (as they are one God) but having a defined relationship in himself. This is the classic issue knows as the "Trinity"—one God in three persons, all fully God not separate beings.

We don't know (because we aren't told) exactly why God is this way, just that he is and this is how he has revealed himself to us. God himself chose to become a man, to reveal himself to us in human flesh, the God-man Jesus Christ—100% God, 100% man.

One famous articulation of this can be found in the Athanasian Creed:

  Neither confounding the persons nor dividing the substance.

  For there is one person of the Father, another of the Son, and another of the Holy Spirit.

  But the Godhead of the Father, of the Son, and of the Holy Spirit is all one, the glory equal, the majesty coeternal.

  Such as the Father is, such is the Son, and such is the Holy Spirit.

  The Father uncreated, the Son uncreated, and the Holy Spirit uncreated.

  The Father incomprehensible, the Son incomprehensible, and the Holy Spirit incomprehensible.

  The Father eternal, the Son eternal, and the Holy Spirit eternal.

  And yet they are not three eternals but one eternal.

  As also there are not three uncreated nor three incomprehensible, but one uncreated and one incomprehensible.

  So likewise the Father is almighty, the Son almighty, and the Holy Spirit almighty.

  And yet they are not three almighties, but one almighty.

  So the Father is God, the Son is God, and the Holy Spirit is God;

  And yet they are not three Gods, but one God.

  So likewise the Father is Lord, the Son Lord, and the Holy Spirit Lord;

  And yet they are not three Lords but one Lord.

Having listened to Pastor Stanley's address, he seems quite clear. You may not like or fully understand what he is saying, but he isn't equivocating or being irrational. His representation of what the Bible says about Jesus is rather accurate and would be agreeable to most Christians of every major sect.

The statement at 21:30 is quite plain but you have taken it out of context. He says "Jesus is not the son of God in the same way that I am the son of my Father". In this section he is defining his terms and making it what he does or does not mean. He goes on to explain how God's existence transcends the physical creation and we only exist in him. Therefor our physical relationship to our fathers is just a small aspect of a son/father relationship and what God means when he says that Jesus is his son is much more than that. All the way up to minute 28 he expands on the idea of God's "begetting" a son transcending our understanding of the physical world.

On a few minor points unrelated to the person of Jesus he wanders a little bit from broadly accepted teachings. For example his theology seems to be dispensational and pre-millenial. His eschatology is not important for this question whether those views are correct or not, but you should be aware that there are differences between major Christian sects on those issues. Likewise the bit in minute 43 about no-cost would be disputed by a number of Christian perspectives.
As for why Jesus prayed, there are several explanations. One is simply that as a man he demonstrated how to live in a proper relationship with God. He was a perfect role model for men and therefore did what men should do. Additionally as one of the persons of the God-head he was in fellowship with his Father.

Of course there are no other superior beings nor churches or temples dedicated to any other in true Christianity because we believe in only one God.


Does Christianity believe in reincarnation?

The Christian Bible says you must be re born to enter heaven.  This is a spiritual rebirth through the acceptance of Christ in your heart.  Christianity does not believe in reincarnation.


"Laughter" has two completely different manifestations: it can be joyous or a cynical sneer.

Joyous laughter: not possible for Satan since Joy is a fruit of The Holy Spirit.

Sneering: not recorded in the Bible from Satan, but certainly used by his followers, see both in the Old Testament (Isaiah 57:3-5) and New when the Pharisees sneered at Jesus, both regarding His attitude to money and His failure (in their perception) to save Himself.

Personal note: I'm pretty sure I can hear the sneering when I read Biblical accounts of Satan, e.g. in his first appearance.


Literal or legend: how do Catholics treat non-Biblical miracles?

If you're interested read more at http://www.catholicbibleanswers.com and let me know what you think

The Catholic Church does consider many miracles outside the Bible to be from God - they are literal miracles

Maybe the most notable miracles are the Marian apparitions (ie., appearances of Mary the mother of Jesus to many individuals across the globe)

Check out: Our Lady of Lourdes apparitions, Our Lady of Guadalupe (this miracle was how South America converted to Christianity about 500 years ago), Our lady of Fatima, etc

There are also many healing miracles


Where in the Bible does it say that sacrifice can only be done on the temple?

The history of the proper locations for offering sacrifices under the Old Testament is like this.

First before Moses sacrifices could be made anywhere.  Then once the tabernacle was built, Moses received the command of the Lord that sacrifices could only be brought to the  “entrance of the tent of meeting” per Lev 17:

  2 “Speak to Aaron and his sons and to all the people of Israel and say to them, This is the thing that the LORD has commanded. 3 If any one of the house of Israel kills an ox or a lamb or a goat in the camp, or kills it outside the camp, 4 and does not bring it to the entrance of the tent of meeting to offer it as a gift to the LORD in front of the tabernacle of the LORD, bloodguilt shall be imputed to that man. He has shed blood, and that man shall be cut off from among his people. (Lev 17:2-4)

The idea is that making your own sacrifice wherever you wanted after the Lord had provided the proper practice within the tabernacle was as bad a shedding blood of a human and therefore punished as severely. However this law did not seem practical when Israel was about to enter Canaan and be always on the move, therefore this restriction was was temporarily repealed by Moses with an eye to a more permanent re-establishment of it in the temple:

First the plan is to establish the rule in the temple:

  5 But you shall seek the place that the LORD your God will choose out of all your tribes to put his name and make his habitation there. There you shall go, 6 and there you shall bring your burnt offerings and your sacrifices, your tithes and the contribution that you present, your vow offerings, your freewill offerings, and the firstborn of your herd and of your flock. (Deut. 12:5-7, ESV)

Then as this is not yet practical, the concession is granted:

  15 “However, you may slaughter and eat meat within any of your towns, as much as you desire, according to the blessing of the LORD your God that he has given you. The unclean and the clean may eat of it, as of the gazelle and as of the deer.
  (Deut. 12:15, ESV).

Finally, as this interim period was come to an end and the Temple was about to be ready to replace the tabernacle, the original Lev 17 ordinance was again resumed. As about just this time, for example, we find the reason why people still sacrificed as ‘high places’:

  2 The people were sacrificing at the high places, however, because no house had yet been built for the name of the LORD. (1 Kings 3:2, ESV)

The ‘high places’ although referred to above as simply meaning a place where people sacrificed offering to God, quickly became an offensive term as not only would sacrificing animals there no longer be tolerated as the Temple after the Temple was built, but this was the place where idolatry was also practices to Baal and Ashera idols. Pagans worship their gods there and just like the golden-calf where Israel mixed up the religion of Jehovah with pagan idolatry, so these ‘high places’ became symbols of the same. When Jews worship there is was a corruption and mixture of God and idols. We see a king doing what ‘is wrong’ as leaving those ‘high places’ in tact.

  43 He walked in all the way of Asa his father. He did not turn aside from it, doing what was right in the sight of the LORD. Yet the high places were not taken away, and the people still sacrificed and made offerings on the high places. (1 Kings 22:43, ESV)

When a King did ‘what is right’ he removed the ‘high places’. In fact this became a litmus-test phrase to distinguish good kings from bad ones.

  19 And Josiah removed all the shrines also of the high places that were in the cities of Samaria, which kings of Israel had made, provoking the LORD to anger. He did to them according to all that he had done at Bethel. 20 And he sacrificed all the priests of the high places who were there, on the altars, and burned human bones on them. Then he returned to Jerusalem. (2 Kings Chapter 23:19-20, ESV)


Why do Catholics recite the phrase "Thanks be to God" during Mass?

It is the English translation of Deo Gratias, which is repeated “in thanksgiving for the graces received at Mass” (Catholic Encyclopedia).


According to Mormons, what is the benefit received from paying tithes and following the temple ceremonies?

Expanding on my comment of

who wants 2nd or 3rd place prize/reward when anyone can have the 1st place prize

The degrees of glory are described in 1 Corinthians 15:40-41

40 There are also celestial bodies, and bodies terrestrial: but the glory of the celestial is one, and the glory of the terrestrial is another.
41 There is one glory of the sun, and another glory of the moon, and another glory of the stars: for one star differeth from another star in glory.

Mormons belive the Celestial kingdom is like the sun, the Terrestrial is like the moon, and the Telestial is like the starts; as a comparison of glory. The Mormons believe that anyone can attain the Celestial Kingdom, which is the only kingdom where we (man) can continue to progress and where we can be in Heavenly Father's (God) and Jesus Christ's presence forever.
I want to answer this question by asking a question in return: Why wouldn't you want to receive all the blessings God has in store for you? God has given us everything and all he asks in return is 10% (tithing) in return and to keep His commandments which he will then bless us for keeping. Man has agency, so it is up to you what commandments to follow or not, and you will be rewarded for what commandments you keep.
See also
Kingdoms of Glory


I'm a practicing Roman Catholic, but considering attending a Greek Orthodox church instead of our local RC church. Will I be welcomed?

I cannot speak for whether the Orthodox will welcome you or not, although I'm fairly sure they'll push for you to convert, that is, formally leave the Catholic Church and join the Orthodox one; depending on the Church, they might even not recognize your baptism as valid and thus require you to be baptized again, though most will allow conversion through chrismation.
Regarding the Catholic Church, however, Canon 844 forbids Catholic faithful to receive Eucharist from non-Catholic ministers except in emergencies:

Can.  844 §1. Catholic ministers administer the sacraments licitly to Catholic members of the Christian faithful alone, who likewise receive them licitly from Catholic ministers alone, without prejudice to the prescripts of §§2, 3, and 4 of this canon, and can. 861, §2.
§2. Whenever necessity requires it or true spiritual advantage suggests it, and provided that danger of error or of indifferentism is avoided, the Christian faithful for whom it is physically or morally impossible to approach a Catholic minister are permitted to receive the sacraments of penance, Eucharist, and anointing of the sick from non-Catholic ministers in whose Churches these sacraments are valid.
§3. Catholic ministers administer the sacraments of penance, Eucharist, and anointing of the sick licitly to members of Eastern Churches which do not have full communion with the Catholic Church if they seek such on their own accord and are properly disposed. This is also valid for members of other Churches which in the judgment of the Apostolic See are in the same condition in regard to the sacraments as these Eastern Churches.
§4. If the danger of death is present or if, in the judgment of the diocesan bishop or conference of bishops, some other grave necessity urges it, Catholic ministers administer these same sacraments licitly also to other Christians not having full communion with the Catholic Church, who cannot approach a minister of their own community and who seek such on their own accord, provided that they manifest Catholic faith in respect to these sacraments and are properly disposed.
§5. For the cases mentioned in §§2, 3, and 4, the diocesan bishop or conference of bishops is not to issue general norms except after consultation at least with the local competent authority of the interested non-Catholic Church or community.

So, if you're somewhere there are no Catholic priests, and you understand that it is better for you as a Catholic to receive the Eucharist from a Catholic priest (even if Eastern) rather than a non-Catholic one, you may go receive it from an Orthodox or Old Catholic or some other kind of non-Catholic priest with a valid Apostolic Succession and Eucharistic prayer.  It doesn't seem to be the case with you, though; so I would recommend looking for an Eastern Catholic parish near your home, where you may participate in Byzantine (or Antiochene, or Alexandrian) Divine Liturgy and remain in the Barque of Peter.
One more point, raised by AthanasiusOfAlex in the comments, is that Divine Liturgy at an Orthodox Church also does not fulfill Sunday obligation (save in the case of some very small Eastern Churches where the Church in question and her Orthodox sister have formally agreed to share priests).
The relevant Canon is 1248:

Can.  1248 §1. A person who assists at a Mass celebrated anywhere in a Catholic rite either on the feast day itself or in the evening of the preceding day satisfies the obligation of participating in the Mass.
§2. If participation in the eucharistic celebration becomes impossible because of the absence of a sacred minister or for another grave cause, it is strongly recommended that the faithful take part in a liturgy of the word if such a liturgy is celebrated in a parish church or other sacred place according to the prescripts of the diocesan bishop or that they devote themselves to prayer for a suitable time alone, as a family, or, as the occasion permits, in groups of families.

Again, all these issues do magically solve themselves if you manage to find an Eastern Rite parish somewhere you can attend; then you may attend Divine Liturgy there and never worry about violating any Canons, or worse, receiving Communion illicitly or invalidly.


Which of these interpretations of Malachi 3:1 can be eliminated?

Actually I don't see the need to try and eliminate various interpretations. How about using some "reasoning" skills/logic to figure out what the Bible says are the messengers.
Isaiah 40:3, "A voice is calling , Clear the way for the Lord in the wilderness; Make smooth in the desert a highway for our God." Mark 1:1-4, "The beginning of the gospel of Jesus Christ, the Son of God. vs2, As it is written in Isaiah the prophet, Behold I send My messenger before your face, Who will prepare Your way;
Verse 3, The voice of one crying in the wilderness, Make ready the way of the Lord, Make His paths straight." Vs 4, "John the Baptist appeared in the wilderness preaching a baptism of repentance for the forgiveness of sins." So we know for a fact the first messenger is John the Baptist. You can also read Luke 3:1-6.
Notice from Isaiah 40:3, "Make smooth a highway for our God." The messenger of the covenant is the preincarnate Jesus Christ known in the Old Testament as "the angel of the Lord." He appears "physically" to the OT saints.
He is also identified as God at various places, "Genesis 16:13, Genesis 22, where He swears to Abraham that He will bless his descendants. And most notably is at Exodus 3 when he appears in the burning bush.
So to sum up the first messenger is John the Baptist. The second messenger is the Lord Jesus Christ who is equated with God and the one who came to "HIS" temple and fulfilled this prophecy.


Is Jesus using a rhetorical device when he says "turn the other cheek"?

Assuming you are referring to Matthew 5:38-42 (NIV) :

  38 "You have heard that it was said, 'Eye for eye, and tooth for
  tooth.' 39 But I tell you, Do not resist an evil person. If someone
  strikes you on the right cheek, turn to him the other also. 40 And if
  someone wants to sue you and take your tunic, let him have your cloak
  as well. 41 If someone forces you to go one mile, go with him two
  miles. 42 Give to the one who asks you, and do not turn away from the
  one who wants to borrow from you.

You could explain this rhetoric, but if we look at the examples He uses, it does not have to be rhetoric but can also be literally. Let's take a look:

If someone hits you on the right cheek, the attacker hopes he won with just one hit (this was usually a hit with the back of the right hand, not very hard, just to scare you off) . If you fight back, you are as low as your attacker, if you do nothing (which he aims for), he wins. However, Jesus tells here: "turn to him the other also". How would the attacker feel right now? He did not win, and he has to hit a second time (this time really on purpose, and if he hits he can now hit hard. (try it once, back of your right hand on someone's right cheek, if he turns his head so you can hit the left you can hit full power)

The second example Jesus gives, is similar. Back in the days of Jesus people wore most of the time only two pieces of clothing, your  tunic and a cloak. If someone asks for your tunic, you know you are naked under your cloak. Which, again, hurts only you and will give you won. But if you do also give your cloak, how would the one requesting for the tunic feel now?

The third example Jesus gives, is similar as well. If you were forced to walk one mile (usually by the legal power), a soldier would go with you to check whether you walked the mile. (often you had to carry a burden as well, but anyways) When you walk just the mile, it hurts only you and you have accepted your punishment. However when you walk an extra mile the soldier checking you walked the mile had a problem, he was not allowed to punish you more than the he was ordered to.

Is Jesus merely saying that we shouldn't seek revenge, or is he advocating pacifism?
I would say Jesus is indeed saying that we should not seek revenge. He challenges us to be smarter than your opponent(probably not the right word) and show them that you are not controlled by him, and therefore not do whatever they tell you, but live for the living God.


Wouldn't the "spirit of Jesus" [mentioned in Acts 16:7] challenge the idea of the Trinity?

PROLEGOMENA

Luke, the writer of the words you quoted from Acts 16, had evidently learned well via the Eleven that the Holy Spirit, while not Jesus, was indeed the Spirit of Jesus within the lives of believers after Jesus had ascended to the Father. During Passion Week, Jesus in John 14 had taught his disciples about the person whom he identified by several names and functions, including

  another helper (or comforter), or simply the helper
  the Spirit of truth
  the Holy Spirit
  the one sent by the Father
  the one who would teach Jesus’ followers and bring to remembrance (after Jesus’ ascension) what he had said while with them for three short years

To speak of the Spirit of Jesus, then, is to speak of the Holy Spirit, and vice versa. Jesus’ teaching on the Holy Spirit made one thing perfectly clear: While he—Jesus—would no longer be with his disciples for a time, they could with full assurance know that 1) Jesus would be coming back again, so that where he was, there they would also be (John 14:3); and 2) the Holy Spirit would be, as it were, Jesus’ surrogate presence with them until they were reunited with Jesus in the Father’s house (John 14:2).

Since there is perfect equality within the Godhead, the Bible frequently alludes to this equality in various ways. For example, "I and the Father are one," Jesus said (John 10:30), by which he meant they were of one divine essence. In Acts chapter 5, Peter accused Ananias of lying to the Holy Spirit (v.3), and in the next verse he told Ananias that he had lied to God. Clearly, Peter equated the Holy Spirit with God.

Each person of the trinity is fully God, with all the attributes of deity. I say this notwithstanding that Jesus, on more than one occasion, seemed to defer to the Father, as when he said, for example,

  My Father, who hath given [my sheep] unto me, is greater than all; and no one is able to snatch [them] out of the Father's hand (John 10:29 ASV).

On another occasion Jesus also said to his disciples,

  You heard that I said to you, “I will go away, and I will come [back] to you.” If you loved me, you would have rejoiced because I go to the Father, for the Father is greater than I (John 14:28).

Jesus' attribution to the Father being "greater than all" does not mean Jesus was or even thought himself to be inferior to the Father in power or in any other way. The point Jesus was making in John 10 was that true believers (i.e., the sheep in Jesus' metaphor) are safely ensconced in the hands of both the Son and the Father. Moreover, both Jesus and the Father are in one accord regarding their plans and purposes for the human race; namely, to call to themselves a people who will be with them forever in heaven and who forever will bear the image of God's only beloved Son, in whom he is well pleased (see Romans 8:29; Matthew 3:17 and 17:5).

According to the Bible, from eternity past, each person in the Godhead has assumed a role, as it were, within the Godhead. Each role is both unique and complementary in the ongoing purposes of all three persons of the Godhead. Moreover, there is unanimity of purpose. Each person will forever be in one accord with the other members of the trinity as to their ongoing, divine motives, intentions, attitudes and actions. Much more could be said about this, but perhaps an illustration might prove helpful.

Just as a baby born into a family begins very early to intuit that each parent is a bit different from the other (if only in their appearance and the sound of their voices), so also in that same family the child will eventually learn that despite the parents having different roles within the family unit, the family is still a unit composed of three equal persons (though very early in life the baby thinks he or she is the center of the universe).

While the father may assume a role which the mother does not assume, the child still intuits that both parents are still parents. At the same time, however, the child relates to each parent in a slightly different way, and vice versa. In a multiple-child family, the same can be said of each child. The parent-child relationship, though it will evolve over time, will always be a human-to-human, parent-child relationship, even if the adult develops dementia and the roles seem to be reversed.

So it is within the Godhead, but on a divine level. Each person—Father, Son, and Holy Spirit, has a role to play, but each person retains his deity and equality within the Godhead. Even when Jesus became a human being via his immaculate and divine conception, his deity was at no time compromised. To be sure, for a time he emptied himself of some of his divine prerogatives, or to put it differently, he veiled his divine nature and attributes, all for the suffering of death (see Philippians 2). At no time, however, did he cease being God.

After Jesus forgave the sins of a paralytic (whom he also healed), even some of Jesus’ detractors were correct when they remarked in Jesus’ presence,

  Who is this man who speaks blasphemies? Who can forgive sins, but God alone? (Luke 5:21; Mark 2:7).

Even though Jesus humbled himself by “taking the form of a bond-servant, and [by] being made in the likeness of men,” he still retained the prerogative of God to forgive sins, not to mention perform miracles, which included raising people from the dead! Moreover—and perhaps more importantly, by being the Lamb of God who became “obedient to the point of death, even death on a cross,” Jesus made the forgiveness of sins possible through his shed blood at Calvary (again, see Philippians 2:7-8).

The doctrine of the trinity is perhaps the most difficult-to-understand doctrine in all of Scripture. Christians may sound as if they are copping out when they say it’s a mystery, but it is, in fact, quite mysterious. How can a God who is described as One Lord in one place (e.g., Deuteronomy 6:4) have in another place a “doubting Thomas” say, without being reproved by Jesus for saying it,

  ”My Lord and my God!” (John 20:28)?

In conclusion, each person in the Godhead, though singularly unique, is in perfect synchronicity with each other person in the Godhead. This fact has been a cornerstone of the Christian faith for centuries, and the teaching was codified in one of Christianity’s most significant creeds, the Athanasian Creed (named after, but likely not written by, Athanasius, the fourth century Bishop of Alexandria), which reads in part,

  [W]e worship one God in Trinity, and Trinity in Unity, neither confounding the persons, nor dividing the substance.

  For there is one Person of the Father, another of the Son, and another of the Holy Spirit. But the godhead of the Father, of the Son, and of the Holy Spirit, is all one, the glory equal, the majesty co-eternal.

  Such as the Father is, such is the Son, and such is the Holy Spirit. The Father uncreated, the Son uncreated, and the Holy Spirit uncreated. The Father incomprehensible, the Son incomprehensible, and the Holy Spirit incomprehensible.
  The Father eternal, the Son eternal, and the Holy Spirit eternal. And yet they are not three eternals, but one Eternal.

  As also there are not three incomprehensibles, nor three uncreated, but one Uncreated, and one Incomprehensible. So likewise the Father is Almighty, the Son Almighty, and the Holy Spirit Almighty. And yet they are not three almighties, but one Almighty.

  So the Father is God, the Son is God, and the Holy Spirit is God. And yet they are not three gods, but one God.


What must a Catholic believe to be a Catholic?

Truths absolutely necessary for salvation
The four truths absolutely necessary to believe for salvation are that

"he [God] is", i.e., that God exists (Heb. 11:6)
God "is a rewarder to them that seek him." (Heb. 11:6)
the Second Person of the Trinity took on a human nature (Incarnation)
God is Three Divine Persons in one God (Trinity)

Note: There is unanimous consent among Catholic theologians that truths #1 and #2 are absolutely necessary to be explicitly believed in order to be saved, but not all theologians (St. Thomas Aquinas, St. Alphonsus Liguori, et al. excepted) think that explicit belief in truths #3 and #4 is necessary; cf. True or False Pope p. 113 // PDF p. 128.source
Truths necessary to be Catholic
To be Catholic, one must, as the asker writes, indeed "believe the articles in the Nicene and Apostolic Creeds and the Ex Cathedra statements about Holy Mary's Immaculate Conception and Assumption" (cf. the 4 Marian dogmas).


Is there any historical evidence that Gnosticism disappeared because Gnostics converted to Christianity?

The Gnostics were already in decline numerically by the third century, but  events brought about the elimination of Gnostic Christianity over  the centuries that followed.

Emperor Constantine
Elaine Pagels says,in Beyond Belief, page 168, that Constantine ordered the return or restitution of property confiscated from the Christian church during the persecutions during the decades leading up to his reign. However, his edict only applied to "to the largest and best organised Christian group" and Constantine excluded the Gnostics. By this means, Gnostics were starved of resources and treated as outside the law. Stephan A. Hoeller says, in Gnosticism, page 156, that With the triumph of orthodox Christianity after Constantine, the Gnostic religion went underground. Hoeller goes on:

  The final blow to early Gnostic Christianity came in the late fourth century, when the wave of fierce persecution burst upon the followers of the Spanish bishop Priscillian of Avila, despite the pleadings of charitable orthodox Christians. From this time on, the ceaseless hunt for Gnostics made it difficult for the Gnosis to survive in western Europe.

Eastern Europe
Richard Smoley says, in Forbidden Faith, pages 69-70, a new sect known as the Bogomils arose in the Balkans, probably as descendants of the Paulicians whom the Byzantine emperor Constantine V had resettled there in 759 CE, hoping they would convert to orthodox Christianity. The Bogomils were driven westward to Dalmatia and Bosnia, where they remained, although persecuted by the dominant Christians, until the fifteenth century. With the arrival of the Ottoman Turks,   many Bogomils converted to Islam, which Smoley says "helps explain why so many Bosnians are Muslims to this day, and why the religious conflicts in the area are still so grievous." The Turks sought to ease the administrative burden by having all Christians in their newly acquired European territories subordinated to the Orthodox Patriarch, but the Bogomils had suffered centuries of persecution by the Orthodox Christians and preferred to be Muslims than subordinated to the hated Patriarch.

Catherism
The Cathars of southern France and Spain had spread through Germany from eastern Europe during the twelfth century.  Smoley (ibid, page 76) says "The number of Catholic priests and monks who were won over to Catharism appears to have been significant."

Pope Innocent III urged the French nobility to suppress the faith, but many nobles refused. Finally, in 1208, Innocent initiated a crusade against the Cathars. The crusade was not enough to stamp out Catharism, even with large numbers of the leaders being burnt at the stake.  Finally, after total military defeat, the Cathar people were forced to demonstrate allegiance to the Catholic Church. An Inquisition was set up, to identify and, if necessary, torture and condemn people found to be practising their old faith in secret.

Conclusion
The historical evidence is that some Gnostics converted to Catholic or Orthodox Christianity, often out of necessity, while others accepted Islam rather than join those who had long persecuted their ancestors.


How does Christ's hypostatic union affect the temporal nature of the Trinity?

Opposites cannot be said truly of the same thing in the same way: the divine and human things said of Christ are, of course, in opposition, suffering and incapable of suffering, for example, or dead and immortal
St. Thomas Aquinas - On the Trinity and the Incarnation Chapter 39

St. Thomas holds that Christs two natures are neither confused nor mixed. And Jesus' body, which has natural properties is subject to them.  Christ's divine nature is not subject to the things that His human nature is subject to.
I think you're thinking that they're mixed somehow and Christ's human nature (and subsequent death) brings down the Trinity or splits it up for a bit.  But that's just not contingent on the Incarnation.    If so, the Trinity would have been affected by the Incarnation as well as by the Crucifixion and It would have been made more glorious by the Transfiguration and even more glorious by the Resurrection.

Furthermore,

It is clear also from this that, although the Son is incarnate, neither the Father nor the Holy Spirit, for all that, need be incarnate, since the Incarnation did not take place by a union in the nature in which the three divine Persons are together, but in hypostasis...

The Trinity is a plurality of Persons subsisting in one nature and the Incarnation is one Person subsisting in a plurality of natures.
So, Trinity and the Incarnations require more than complicated Venn Diagrams to explain.

  +-----------------+   (Incarnation)
 +                   +       |
 +      Father    +--+-------|---+
 +        +------+DN +--+    |    +
  +------+-------+--+    + Son HN +
         + Spirit+       +   |    +
         +               +---|---+
          +-------------+    |

DN = divine Nature
HN = Human Nature
but an even better than a crummy ASCII venn diagram is every piece of religious art depicting Jesus ever

where you see Jesus' hand with two fingers and a thumb up representing the Blessed Trinity and two fingers down representing His two natures.


What is the Jehovah's Witness perspective on salvation?

Jehovah's Witnesses believe in salvation by means of faith in Jesus Christ, and that we demonstrate that faith by being obedient to Jesus' commands.

I don't think I could describe it any better than the article on jw.org: What Is Salvation?

The article summarizes the cited scriptures, but to fully understand what Jehovah's Witnesses believe, you really need to read those scriptures. If you read the article directly from jw.org, the little dialog boxes make looking up the scriptures much easier.

  What Is Salvation?

  The Bible’s answer

  The terms “save” and “salvation” are sometimes used by Bible writers to convey the idea of a person’s being delivered from danger or destruction. (Exodus 14:13, 14; Acts 27:20) Often, though, these terms refer to deliverance from sin. (Matthew 1:21) Since death is caused by sin, people who are saved from sin have the hope of living forever.—John 3:16, 17.

  What is the way to salvation?

  To gain salvation, you must exercise faith in Jesus and demonstrate that faith by obeying his commands.—Acts 4:10, 12; Romans 10:9, 10; Hebrews 5:9.

  The Bible shows that you must have works, or acts of obedience, to prove that your faith is alive. (James 2:24, 26) However, this does not mean that you can earn salvation. It is “God’s gift” based on his “undeserved kindness,” or “grace.”—Ephesians 2:8, 9; King James Version.

  Can you lose out on salvation?

  Yes. Just as a person saved from drowning could fall or jump back into the water, a person who has been saved from sin but fails to keep exercising faith could lose out on salvation. For this reason, the Bible urges Christians who have received salvation “to put up a hard fight for the faith.” (Jude 3) It also warns those who have been saved: “Keep working out your own salvation with fear and trembling.”—Philippians 2:12.

  Who is the Savior—God or Jesus?

  The Bible identifies God as the primary source of salvation, often referring to him as “Savior.” (1 Samuel 10:19; Isaiah 43:11; Titus 2:10; Jude 25) In addition, God used various men to deliver the ancient nation of Israel, and the Bible calls them “saviors.” (Nehemiah 9:27; Judges 3:9, 15; 2 Kings 13:5) Likewise, since God provides salvation from sin through the ransom sacrifice of Jesus Christ, the Bible refers to Jesus as “Savior.”—Acts 5:31; Titus 1:4.

  Will everyone be saved?

  No, some people will not be saved. (2 Thessalonians 1:9) When Jesus was asked, “Are those being saved few?” he replied: “Exert yourselves vigorously to get in through the narrow door, because many, I tell you, will seek to get in but will not be able.”—Luke 13:23, 24.

Here are some more related questions answered on jw.org:

Does the Bible Teach ‘Once Saved, Always Saved’?
Do Jehovah’s Witnesses Feel That They Are the Only People Who Will Be Saved?


According to Catholicism, why does Paul spend so much time arguing that the law doesn't apply, when Jesus seems to indicate that it does?

Acording to the Catechism of the Catholic Church (as usual, emphasis is mine):

577 At the beginning of the Sermon on the Mount Jesus issued a solemn warning in which he presented God's law, given on Sinai during the first covenant, in light of the grace of the New Covenant:

Do not think that I have come to abolish the law or the prophets: I have come not to abolish but to fulfill. For truly I tell you, until heaven and earth pass away, not one letter, not one stroke of a letter, will pass from the law, until all is accomplished. Therefore, whoever breaks one of the least of these commandments, and teaches others to do the same, will be called least in the kingdom of heaven; but whoever does them and teaches them will be called great in the kingdom of heaven.

So far, so good: it is as the OP has commented. Jesus himself says that he has come to "fulfill" and not to "abolish" the law.

578 Jesus, Israel's Messiah and therefore the greatest in the kingdom of heaven, was to fulfill the Law by keeping it in its all embracing detail — according to his own words, down to "the least of these commandments". He is in fact the only one who could keep it perfectly. On their own admission the Jews were never able to observe the Law in its entirety without violating the least of its precepts. This is why every year on the Day of Atonement the children of Israel ask God's forgiveness for their transgressions of the Law. The Law indeed makes up one inseparable whole, and St. James recalls, "Whoever keeps the whole law but fails in one point has become guilty of all of it."

Here the Church points out that no one, save the Son of God, was able to keep all of the law, and the Jewish ceremony of Yom Kippur testifies to that. At the same time, the Law is whole and indivisible: there cannot be multiple levels of compliance with the Law.

580 The perfect fulfillment of the Law could be the work of none but the divine legislator, born subject to the Law in the person of the Son. In Jesus, the Law no longer appears engraved on tables of stone but "upon the heart" of the Servant who becomes "a covenant to the people", because he will "faithfully bring forth justice". Jesus fulfills the Law to the point of taking upon himself "the curse of the Law" incurred by those who do not "abide by the things written in the book of the Law, and do them", for his death took place to redeem them "from the transgressions under the first covenant".

Through Jesus's death, the Perfect Sacrifice, the Law is fulfilled, and thus the penalty for failing to uphold the Law is paid by Him. Thereafter, those who believe in Him can point to that Sacrifice as reparation for their transgressions of the Law.

581 The Jewish people and their spiritual leaders viewed Jesus as a rabbi. He often argued within the framework of rabbinical interpretation of the Law. Yet Jesus could not help but offend the teachers of the Law, for he was not content to propose his interpretation alongside theirs but taught the people "as one who had authority, and not as their scribes". In Jesus, the same Word of God that had resounded on Mount Sinai to give the written Law to Moses, made itself heard anew on the Mount of the Beatitudes. Jesus did not abolish the Law but fulfilled it by giving its ultimate interpretation in a divine way: "You have heard that it was said to the men of old. . . But I say to you. . ." With this same divine authority, he disavowed certain human traditions of the Pharisees that were "making void the word of God".

Jesus did not abrogate the Law, but fulfilled it, by going above the conventional Rabbinic interpretations of Scripture, but by teaching them directly. His teachings are fully compatible with Mosaic Law, but are above them as perfectly realised expressions of the will of God.

582 Going even further, Jesus perfects the dietary law, so important in Jewish daily life, by revealing its pedagogical meaning through a divine interpretation: "Whatever goes into a man from outside cannot defile him. . . (Thus he declared all foods clean.). . . What comes out of a man is what defiles a man. For from within, out of the heart of man, come evil thoughts. . ." In presenting with divine authority the definitive interpretation of the Law, Jesus found himself confronted by certain teachers of the Law who did not accept his interpretation of the Law, guaranteed though it was by the divine signs that accompanied it. This was the case especially with the sabbath laws, for he recalls, often with rabbinical arguments, that the sabbath rest is not violated by serving God and neighbor, which his own healings did.

Here, we are reminded of the instances in the Gospels where Jesus seems to invalidate or abrogate Mosaic Law, but instead perfects it, returning it to its original spirit.
And because the observance of the letter of the Law interfered with its spirit, St. Paul reasoned that the Gentiles should not be forced to uphold it. Recall that St. Paul himself observed the precepts of the Law just as much as when he persecuted Christians (cf. Phillipians 3), as he was Hebrew himself, but that the insistence in following Jewish customs might cause Gentiles to deviate from Jesus's teachings to Moses's, which would be putting the cart before the horse (cf. Acts 15).
Thus the Church sees no contradiction in Jesus's position that he fulfilled the Law and Paul's position that following the Law is not necessary for justification in Christ.


In what way does God derive pleasure from us?

I would only speculate from scripture a few simple answers. It is apparent that in Christianity it is important that we identify God as our "Father" through Christ, in fact it is God's will that we know him as our Father through Christ so it is apparent that God wanted children. God is love and he loves his servants the angels but what greater vessel for him to pour his love into than if he were to have children?  The bible says we are heirs of God, so he being a infinitely wealthy king wanted heirs to bless and shower in his dazzling riches. It brings him pleasure to give his children there good pleasure just as a earthly father gets pleasure in his children's delight.

In short God did not just want servants that will worship him, he wanted a family to love and be loved by (of there own free will).


According to Catholicism, did Jesus have a Guardian Angel?

We see not one but many angels, administering to Jesus , for instance after the temptations in the wilderness:

Then the devil left him, and suddenly angels came and waited on him. - (Mtt 4: 11)

But we see only one angel giving comapany to him at the Garden of Gethsemane:

He withdrew about a stone’s throw beyond them, knelt down and prayed,  “Father, if you are willing, take this cup from me; yet not my will, but yours be done.”  An angel from heaven appeared to him and strengthened him. - (Lk  22: 41-43).

This angel is named as Chamuel in the traditions. "This angel performed a vital ministry for Christ just prior to His going to the cross to die for the sins of humankind," writes Ron Rhodes in his book Angels Among Us: Separating Fact from Fiction. (Courtesy: Learn Religions.com)
We also see that Jesus was in a position to seek physical protection by the angels, when he was being arrested and taken away by the soldiers:

With that, one of Jesus’ companions reached for his sword, drew it out and struck the servant of the high priest, cutting off his ear. “Put your sword back in its place,” Jesus said to him, “for all who draw the sword will die by the sword.  Do you think I cannot call on my Father, and he will at once put at my disposal more than twelve legions of angels? - (Mat 26:51-53).

So, the scriptures  do not as such say that Jesus had a Guardian Angel attached to him, but being Son of God, he had the services of many angels  at “short notice”.
PS: I am not aware if any Catholic Theologian or Mystic has made an authentic statement on the subject.


According to Catholic teaching, what constitutes a prophecy to be Messianic?

It appears that the Church's typological approach to interpreting Messianic prophecy is grounded for the most part in the New Testament information that is later referenced to Old Testament passages. What is primarily considered to be 'Messianic' in nature is largely attributed to that which refers, in hindsight, to Christ, who is in fact the Messiah. The Jewish considerations throughout the years of these same passages as prophecy is a secondary, though important point as well. A helpful link that includes a somewhat extensive and easy to access list of the New Testament verses that either reference or can be referenced to particular Old Testament passages that are typological in nature can be found here. The following will address the latter point, in regards to whether Jewish culture likewise used typology and if so in what way.

Jewish Typology

The question to be answered in addition to the Christian typology is naturally whether the Jewish culture around this time both approached Scripture typologically and applied such an approach to their own understanding of what was to come. We could of course refer to Scripture itself, which appears to maintain a typological approach within its own text. The following are a few examples:

  Unless the LORD Almighty had left us some survivors, we would have become like Sodom, we would have been like Gomorra. Hear the word of the LORD, you rulers of Sodom; listen to the law of our God, you people of Gomorra! (Isaiah 1.9)
  Go now to the place in Shiloh where I first made a dwelling for my Name, and see what I did to it because of the wickedness of my people Israel. While you were doing all these things, declares the LORD, I spoke to you again and again, but you did not listen; I called you, but you did not answer. Therefore, what I did to Shiloh I will now do to the house that bears my Name, the temple you trust in, the place I gave to you and your fathers. I will thrust you from my presence, just as I did all your brothers, the people of Ephraim. (Jeremiah 23.14)
  Everyone who quotes proverbs will quote this proverb about you: "Like mother, like daughter." You are a true daughter of your mother, who despised her husband and her children; and you are a true sister of your sisters, who despised their husbands and their children. Your mother was a Hittite and your father an Amorite. Your older sister was Samaria, who lived to the north of you with her daughters; and your younger sister, who lived to the south of you with her daughters, was Sodom. You not only walked in their ways and copied their detestable practices, but in all your ways you soon became more depraved than they. (Ezek 16.44)
  Isaac prayed to the LORD on behalf of his wife, because she was barren. The LORD answered his prayer, and his wife Rebekah became pregnant. The babies jostled each other within her, and she said, "Why is this happening to me?" So she went to inquire of the LORD.
  The LORD said to her, "Two nations are in your womb, and two peoples from within you will be separated; one people will be stronger than the other, and the older will serve the younger." (Genesis 25)
  The LORD will dry up the gulf of the Egyptian sea; with a scorching wind he will sweep his hand over the Euphrates River. He will break it up into seven streams so that men can cross over in sandals. There will be a highway for the remnant of his people that is left from Assyria, as there was for Israel when they came up from Egypt. (Exodus 14.6)
  As in the days when you came out of Egypt, I will show them my wonders (Micah 7.13)

All of these verses show both examples of interpreting present situations in terms of past events and predictive cases in which a certain 'type' is indicative of what will occur in the future. Thus, one commentator states "the data from the OT shows quite clearly that typology was a mainstream interpretive approach to Israel's history , personages, events and primeval history. Accordingly, NT writers were not employing an 'alien' method to the exegesis of the OT-- indeed, they were squarely in the mainstream of accepted hermenuetical approach." This indicates that what often appears to be simply historical reference (as certain Messianic prophecies are) can be taken to be, or implied to be in the writing itself, another thing entirely.

Though an objective fact itself, it can also be written in hyperbole, or talking about a very public and/or mystic figure, by which a future tense and further meaning is meant to be taken. These passages can be identified, if they are Messianic especially, as referring to a mystical king or one who is meant to restore some truth and balance. Thus, in the Messianic prophecies we have, the Church is employing an approach very common to Jewish understanding about passages that seem to qualify as speaking in a language of 'types'. This of course does not make these passages 'prophetic' however. It should be noted though that prophecies can very well be formulated in a typological way, meaning that in speaking about a certain historical king, a prophet can stress certain truths that shall occur to a kingly figure beyond the king being apparently spoken about in the actual text. This is very evident in the many passages of prophecy regarding King David and the relation to the Messiah.


Did some Christian sects ever hold the opinion that ritual slaughter was obligatory, before the 10th century?

I do not know if this response will actually answer your question, but I will give it a possible conclusion to it.

In a sense animal sacrifice and ritual slaughter are not always clearly seen or defined, yet it would seem inappropriate to have a animal sacrifice without a set ritual for slaughtering such animals.

  Rituals of animal sacrifice have been far more common in Christianity than is generally recognized. When missionaries arrived in Britain around the year 600, sacrifice was so deeply engrained in culture that the Pope allowed it to continue provided that the animals were offered to the Christian God and no other. In more recent centuries, these rituals have been mainly confined to Eastern Orthodox Churches. An ancient sacrificial liturgy known as the matal, meaning ‘something tender’, has persisted In the Armenian Church to the present day.

  A key requirement of animals offered for sacrifice is that they must be unblemished, ensuring that they have been well-fed, comfortably accommodated and free from disease. In the Armenian matal, at least three factors minimize the suffering caused to the animal during slaughter: rules must be observed, attentiveness shown by the slaughterer, and reverence displayed at all times. In some accounts of sacrifice, the animal is presented as so contented that it co-operates in its own sacrifice. Paulinus (354-431) describes such an instance at the shrine of Felix of Nola in southern Italy, in which a heifer designated for sacrifice guided her owners to the shrine to present herself with them. - Christian Attitudes to Animals

There is the Armenian Matagh tradition that persists to this day. It should be noted that according to tradition, Armenia became a Christian nation in the Year of Our Lord 301.

  In Armenian Christian tradition, matagh (Armenian: մատաղ mataġ) is a lamb or a rooster slated for sacrifice to God, a ritual which has continued from the pagan past. In many regions of Armenia today, this pagan-Christian synthesis is very much alive in the regular slaughter of chosen animals in front of churches. Matagh is done often to ask God for either forgiveness, health, or to give them something in return. People generally gather at the house where the Matagh was done, where they pray and eat the meat. Tradition holds that the meat must be eaten before sundown.

It is not impossible that the Ethiopian tradition of slaughtering animals while saying the trinitarian formula predates the 10th century.

  In the 7th century the conquests of the Muslim Arabs cut off the Ethiopian church from contact with most of its Christian neighbours. The church absorbed various syncretic beliefs in the following centuries, but contact with the outside Christian world was maintained through the Ethiopian monastery in Jerusalem. - Ethiopian Orthodox Tewahedo Church

Wikipedia has this to say about Christian dietary laws:

  Slaughtering animals for food is often done with the trinitarian formula. Although the Armenian Apostolic Church, among other Orthodox Christians, have rituals that "display obvious links with shechitah, Jewish kosher slaughter." In addition, meat consumed by Christians should not retain any blood, a practice that both Jewish and Islamic methods of slaughter also prescribe, and one that is done by most slaughterhouses throughout Christendom. - Christian dietary laws

Today this tradition can still be seen in Ethiopia, the only question is as to when this tradition was first implicated.

  In Addis Ababa, there is one Christian slaughterhouse and one Muslim one, each of which supplies all respective butchers and restaurants. At the Christian slaughterhouse, an Orthodox priest will bless all the animals with a Trinitarian blessing, a pattern that is repeated in other large towns and cities. In the countryside, this may be left to the senior male householders who pray a Trinitarian blessing over the bull, goat, lamb or chicken before its throat is cut. - Food & Fasting


Where in the Catechism can one read about sins of omission?

The place to look is in the online index: within the list for O, look for omission.
The word is found in four paragraphs:

1853 Sins can be distinguished according to their objects, as can every human act; or according to the virtues they oppose, by excess or defect; or according to the commandments they violate. They can also be classed according to whether they concern God, neighbor, or oneself; they can be divided into spiritual and carnal sins, or again as sins in thought, word, deed, or omission. the root of sin is in the heart of man, in his free will, according to the teaching of the Lord: "For out of the heart come evil thoughts, murder, adultery, fornication, theft, false witness, slander. These are what defile a man." But in the heart also resides charity, the source of the good and pure works, which sin wounds.

2277 Whatever its motives and means, direct euthanasia consists in putting an end to the lives of handicapped, sick, or dying persons.
It is morally unacceptable.
Thus an act or omission which, of itself or by intention, causes death in order to eliminate suffering constitutes a murder gravely contrary to the dignity of the human person and to the respect due to the living God, his Creator.
The error of judgment into which one can fall in good faith does not change the nature of this murderous act, which must always be forbidden and excluded.

2284 Scandal is an attitude or behavior which leads another to do evil. the person who gives scandal becomes his neighbor's tempter. He damages virtue and integrity; he may even draw his brother into spiritual death. Scandal is a grave offense if by deed or omission another is deliberately led into a grave offense.

The last, 2326, merely repeats the gist of 2284 in the chapter summary.
The subject might also occur in other places, but these specifically mention omission.


Are there any surviving writings by Marcion or is everything we know of him what his enemies wrote of him?

As is the case for most non-orthodox authors in the early church, none of Marcion's major writings survive, as the Encyclopedia of Ancient Christianity writes:

Since his writings have been lost over time, the information that we have on the life and works of Marcion has reached us through indirect sources, from the
numerous writings of his opponents.

Thus our primary sources are Justin Martyr, Irenaeus, and Tertullian, particularly Tertullian's Against Marcion, which frequently cites Marcion's Antithesis.
However, we do have several brief texts of "Marcionite" origin, which were likely written by either Marcion or one of his followers.  They are the "Marcionite Prologues," short prologues to the Pauline epistles, found in some Latin manuscripts (including a sixth-century codex).  They were first argued to be Marcionite by De Bruyne in 1907, and Harnack adopts his position, based on how they describe Paul's efforts in each letter.  For example, the prologue to Romans reads:

Romani sunt in partibus Italiæ. hi præventi sunt a falsis apostolis et sub nomine domini nostri Jesu Christi in legem et prophetas erant inducti. hos revocat apostolus ad veram evangelicam fidem scribens a Corintho.
The Romans are in the regions of Italy. They had been reached by false apostles and under the name of our Lord Jesus Christ they were led away into the law and the prophets. The apostle calls them back to the true evangelical faith, writing to them from Corinth. (translation source; emphasis added)

It's by no means certain that Marcion actually wrote these prologues, but Harnack and others believe them to be very old and likely written by followers of Marcion – not his opponents.


Does 2 Timothy 1:9 prove the Doctrine of Election?

No. Even as a Calvinist, one has to understand that it takes more than one verse to put together a complete picture of how we understand salvation to work. The verse you reference in Timothy is indeed very helpful, but it really only proves the part about his purpose as the author of salvation was conceived before we were.

In order to defend the doctrine of election, you will need to reach out to other parts of scripture. For example in 2nd Timothy, how do you know that "us" is specific to individuals and not just representative of a general group of "somebodies" that God planned on saving?

I do think the doctrine can be defended from Scripture, but I don't think you can do it from one verse. You need to take into consideration the whole counsel of Scripture.


Would aliens invalidate Christianity as we know it?

It wouldn't change Christianity it all.  The Bible does not suggest that it contains all knowledge and all revelation.  There is a lot it does not reveal.

The presence of other intelligent life elsewhere in the universe would not change our own reality, which includes the following:

The Eternal Triune God created the universe of time, space and matter and everything in it.
Mankind was created in the image of God.  (Genesis 1:26-27)
Mankind sinned against God and thereby incurred God's punishment.  (Genesis 3)
God the Son, the Third Person of the Trinity, entered into creation through the virgin birth and then received the name Jesus (Yeshua/God saves).
Jesus died on the Cross to take upon Himself the punishment incurred by us.
By faith in Jesus, Christ's work on the Cross is credited to our account, freeing us from the penalty of sin and making us sons and daughters of God.
There is a final judgment for every person where those who follow Christ are rewarded and those who reject Christ will pay the penalty for sin themselves.

This is the reality for us.  The reality for other intelligent life would have no impact on our reality, other than that our reality would acknowledge that there was other intelligent life.

Is it impossible for God to enter into His creation again?  No.  It wouldn't matter to us if He did, though.

So, no, Christianity would not change at all.


Is it possible for a married Catholic to be invincibly ignorant that adultery is gravely wrong?

A (validly) married Catholic cannot be invincibly ignorant of the sinfulness of adultery because marriage consent, "the efficient cause of matrimony" (Summa Theologica suppl. q. 45 a. 1), is consent to "the union of persons directed to one purpose" (ibid. ad 2; cf. q. 44 a. 1), or as Canon Law expresses it:

1917 CIC 1081 (1983 CIC 1057)

Matrimonial consent is an act of the will by which each party gives and accepts perpetual and exclusive rights to the body, for those actions that are of themselves suitable for the generation of children.

Regarding ignorance:

1917 CIC 1082 (1983 CIC 1096)

In order that matrimonial consent be considered [valid], it is necessary that the contractants at least not be ignorant that marriage is a permanent society between a man and woman for the procreation of children.

This ignorance is not presumed after puberty.

cf. Summa Theologica II-II q. 154 a. 2 "Whether simple fornication is a mortal sin?"


Where does Augustine say that Adam and Eve were in Eden for just six hours before sinning?

Did Augustine say six hours, and if so, where?

Probably not.

  Finally, Calvin erroneously claims Augustine for the view that Adam
  and Eve fell after a mere six hours. (emphasis added)

This is from John Calvin: Student of the Church Fathers1 in which Lane references Saint Augustin dans l’oeuvre de Jean Calvin2

1. John Calvin: Student of the Church Fathers (Anthony N. S. Lane, A&C Black, Jan 1, 1999, p.220)
2. Saint Augustin dans l’oeuvre de Jean Calvin (Luchesius Smits,
 Van Gorcum, 1957)


What is an overview of the early Church's viewpoints on Christology at the time of the Apostolic Era?

This has been interpreted many ways. And it is made all the more challenging by questions regarding who wrote which documents and when. For purposes of this response, I will assume the entirety of the New Testament was written by AD 100, the history in Acts is reliable, and that Polycarp represents the last surviving Christian leader who was an immediate successor to the apostles.
There is clearly much more that what known by the apostles than has been preserved in the handful of documents we have from their time.
Let's look at a few passages by decade.
The 30s
The creed preserved in 1 Corinthians 15:3-8 is held by conservative and liberal scholars alike to date to the 30s. A few key statements:

Christ died for our sins according to the scriptures; And that he was
buried, and that he rose again the third day according to the
scriptures:

Indicating a belief that Jesus died for sin and rose again--and that His work was prophesied in the Tanakh.
The 40s
I personally date the Gospel of Matthew to the 40s, but I recognize I'm in a minority position here. If we include Matthew, then already in the 40s Jesus is being called Emmanuel.
Acts 10 records a sermon by Peter with the following relevant highlights:

Jesus is Lord of all (vs. 36)
God anointed Jesus (vs. 38)
God was with Jesus (vs. 38)
God raised Jesus from the dead and Jesus appeared (vs. 40-41)
Jesus is our Judge (vs. 42)

The 50s
Here we have the bulk of Paul's teachings, including the extended sermon on the resurrection in 1 Corinthians 15, and the very high-Christology of Romans. Paul regularly refers to Jesus as Lord, and many understand Romans 9:5 to refer to Jesus as God.
1 example from 1 Cor. 15:

28 And when all things shall be subdued unto him, then shall the Son
also himself be subject unto him that put all things under him, that
God may be all in all.

This is a potent claim! All things will be subject to Christ.
The 60s
Assuming Hebrews and Colossians date to the 60s, here we have some of the highest Christology in the New Testament.
From Colossians 1:

16 For by him were all things created, that are in heaven, and that
are in earth, visible and invisible, whether they be thrones, or
dominions, or principalities, or powers: all things were created by
him, and for him:
17 And he is before all things, and by him all things consist.
18 And he is the head of the body, the church: who is the beginning,
the firstborn from the dead; that in all things he might have the
preeminence.

From Hebrews 1:

8 But unto the Son he saith, Thy throne, O God, is for ever and ever:
a sceptre of righteousness is the sceptre of thy kingdom.

Indicating, among other things, that Jesus is the creator, all things consist by him, and that His status as Deity is not in doubt.
Pre-100
Dates here are more controversial, so I'm using a range. I'll cite passages from 3 books that date to this era.

Jesus saith unto him, I am the way, the truth, and the life: no man
cometh unto the Father, but by me. (John 14:6)

(to be sure, I have no problem with the idea that Jesus said this in the 30s; this text reflects that Christians were repeating these words at this time)

That which was from the beginning, which we have heard, which we have
seen with our eyes, which we have looked upon, and our hands have
handled, of the Word of life; (1 John 1:1)

In the beginning was the Word, and the Word was with God, and the Word
was God. (John 1:1)

Since I just quoted one of the most contested passages in scripture, I'll let these verses speak for themselves =). I'll at least try not to take sides but stick to the question.
Also during this period we get clear statements against Docetism--meaning the idea that Jesus didn't really come in the flesh was something that was being said by some--and refuted by authoritative individuals. I have written on this subject here.
Early 2nd century
Ignatius wrote 7 epistles circa 107 as he was en route to Rome to be executed. In his Epistle to the Ephesians, chapter 7:

There is one Physician who is possessed both of flesh and spirit; both
made and not made; God existing in flesh; true life in death; both of
Mary and of God; first passible and then impassible — even Jesus
Christ our Lord.

Polycarp quotes the documents of the New Testament extensively, so much of his work would be a repeat of the sections above.  Two points worth making from Polycarp's epistle to the Philippians (circa AD 107):

He repeatedly refers to "God and Christ"
In chapter 12 he says:

But may the God and Father of our Lord Jesus Christ, and Jesus Christ
Himself, who is the Son of God, and our everlasting High Priest, build
you up

Although Polycarp lived nearly another half-century, we regrettably do not have any other surviving works by him.
Both Ignatius and Polycarp were taught by apostles. Their writings indicate respecting Jesus as God, but also acknowledging a distinction between God the Father and Jesus.
Specific questions from the OP

uppercase God & 2) lowercase god: there is no distinction between majuscules and miniscules in the manuscripts of the time, so no difference would exist between "God" and "god" in these writings--this is an interpretation of the text, not an explicit repetition of the text. That Jesus is called God is found in Hebrews, John, and Ignatius, to name a few.

a powerful pre-existent but created being: The Colossians passage referred to Jesus as the beginning and the creator. Much debate could surely ensue about what the beginning means. John 1:1, John 8:58, and Hebrews 1:2 are commonly cited as evidence of Jesus' pre-mortal existence. This remains a debate in New Testament interpretation to this day, but at the very least we can safely say that the texts used in these debates were in circulation during the apostolic era.

just a human: I find no references to support this view, except on the lips of Jesus' enemies.

Theological development
If the Gospel of John reliably preserves the teachings of Jesus, then the idea of theological development transforming Christian thought between the 30's and the 90's is unsound. The Christology of the apostles themselves stayed right around the same place from ~Pentecost until the end of the century.
If the Gospel of John is a late, unreliable document (this is not my view), then at the very least, we've got full on high Christology within a few years of AD 60, well within the lifetimes of multiple apostles and numerous eyewitnesses.
Once upon a time I created a video pointing out the flaws in trying to introduce patterns of changing theology in the New Testament. That video can be found here.
My own studied view with respect to Christology & chronology is that the highest Christology in the New Testament is fully consistent with what the apostles believed in the early 30s; they didn't teach the most profound doctrines until they'd laid a "milk before meat" foundation, which is why so many early documents do not contain some of the more potent teachings by Jesus about who He was. I have a post on SE-Hermeneutics discussing this specifically with respect to the Gospel of John.
Some wish to say New Testament theology shows a sequence of development between the 30s and the 90s--I disagree. I believe major changes in Christian understanding of theology happened:

Between Jesus' baptism and Pentecost
After the apostles were gone

Concluding thoughts
The writings of the apostles and their immediate successors suggest that from very early on, Christianity was plagued with diverse doctrines. I see in the teachings of the apostles themselves, however, that Jesus was Divine and that He was distinct from the Father. Both of those principles have been reworked many times over the millennia to produce a variety of theologies that were not taught by the apostles.
What about the later creeds? From Harper's Bible Dictionary:

the formal doctrine of the Trinity as it was defined by the great
church councils of the fourth and fifth centuries is not to be found
in the [New Testament] (see here p. 1099)

So the creeds aren't there in the first century, but the most significant passages that would be used to support many theologies over the years (which surely is not what the apostles wanted) were all there within the first century.
This is a difficult topic upon which to give an even-keel overview. My own beliefs are described here.


Was Luke an eye-witness to the crucifixion?

There are two issues here. The first one is that Luke is not mentioned as an eyewitness to the crucifixion and, being a companion to Paul in the fifties, more than twenty years later, was unlikely to have been an eyewitness. The second issue is that Luke the physician is unlikely to have been the author of the gospel that now bears his name.

Eyewitness to the crucifixion

Mark's Gospel tells us that the women who knew Jesus watched from afar off, with no mention of Luke, or of the disciples

  Mark 15:40: There were also women looking on afar off: among whom was Mary Magdalene, and Mary the mother of James the less and of Joses, and Salome.

Matthew's Gospel (Matthew 27:55) agrees with Mark that only women watched from a distance. Luke's Gospel is more ambiguous, allowing that the little group might have included men, but with no mention of names (and certainly no mention of Luke):

  Luke 23:49: And all his acquaintance, and the women that followed him from Galilee, stood afar off, beholding these things.

Composition of Luke's Gospel

All the New Testament Gospels were written anonymously. The Gospel now known as Luke's Gospel was attributed to Luke during the second century, apparently on the basis that it appeared to have been written by a gentile, and the same author wrote Acts of the Apostles, which was thought to point to a close acquaintance of Paul as the author.

'Luke' opens the gospel by assuring Theophilus of the veracity of his account. Presumably if he had been present in Jerusalem, or if he had researched the facts about Jesus, or even received his gospel knowledge from Paul, he would have said so, but he does not. If he had learnt it from a reliable witness to the the mission of Jesus, he would also have said so, at the same time declaring this to be clear evidence of the gospel's reliability. Instead, he merely says that the gospel came to him through prior sources, the first of whom was [presumably] an eyewitness:

  Luke 1:2: Even as they delivered them unto us, which from the beginning were eyewitnesses, and ministers of the word;

It is the almost unanimous consensus of critical scholars that Mark's Gospel was one of Luke's sources, with a strong but less overwhelming consensus that the hypothetical 'Q' document was another of the sources to which he refers in the prologue. John Dominic Crossan says in The Birth of Christianity, page 93, that he spent the 1960s in a monastery, poring over the gospels in parallel columns, word after word and unit after unit, day after day and year after year, studying the scholarly hypothesis and doing source-criticism. In the end he found it absolutely convincing.


What does St. Augustine mean by predestination?

As the quotation in the body of your question points out, St. Augustine deduced from the New Testament texts the following definition: "Predestination is the foreknowledge and the preparation of those gifts of God whereby they who are delivered are most certainly delivered."(1) In this definition the word "foreknowledge" is not taken as meaning that God foresees the merits of the elect, but that He foreknows and prepares the gifts by which the elect will actually be saved in the order of execution. "By His predestination, God foreknew what He had to do,"(2) so as to direct His elect infallibly to eternal life.  Here Augustine is echoing our Lord's words: "My sheep . . . shall not perish for ever. And no man shall pluck them out of My hand." (3)

According to St. Augustine, predestination presupposes a decisive and definite will on God's part to sanctify and freely save all the elect. (4) God knows them individually and He wills to have them perform meritoriously acts that are required for entering heaven. He wills to give them the grace to persevere until the end.  “..It is God who worketh in you, both to will and to accomplish according to His good will."(5) The fact that God foresees our salutary and meritorious acts presupposes, according to the teaching of St. Augustine, the decree of the divine will as regards these acts. (6)

  Far be it that man should have the power to frustrate the intention
  of the omnipotent Being who has foreknowledge of all things.  These
  have but a faint conception of so great a question or what they have
  does not suffice, who think that the omnipotent God wills something
  and is powerless to effect it because of weak man preventing Him.

Augustine says that God’s will is omnipotent and efficacious (most efficacious).(7) We read in one of his treatises as follows: "There is no doubt that human wills cannot resist (in sensu composito) the will of God, who hath done whatsoever He willed in heaven and on earth, in that He does what He wills and when He wills. Undoubtedly He has the power to move the human heart to submit, as it pleases Him, to His omnipotent will."(8) From this we see that, in St. Augustine's view, the decrees of the divine will are infallible not because God foreknows that we will give our consent, but because He is omnipotent. He also says: "The wills of men are more in God's power than in their own."(9) In another of his works he says: "There is no doubt that we will whenever we will, but He is the cause of our willing what is good; . . . there is no doubt that we act whenever we act, but He is the cause of our acting, by most efficaciously strengthening our will."(10) Still more clearly when speaking professedly on this subject of predestination, he says that "no one who is hardened in heart rejects grace, because it is primarily given to remove this hardness of heart.''(11)

St. Augustine repeatedly teaches and stresses that predestination is gratuitous. In discussing the gift of perseverance, he says: "Of two children equally held captive by original sin, why is one taken and the other left? And of two wicked persons already advanced in years, why is one called and the other not? All this pertains to the inscrutable judgments of God."(12) He also says: "Why God draws this one and not that other, seek not to judge, if thou wilt not err."(13) What precisely constitutes the crux of the mystery, according to St. Augustine's opinion, is man's inability to find out the reasons for the divine choice. He is continually harking back to this impossibility, and his opponents find no avenue of escape from it. This impossibility is a pledge of his fidelity to the teaching of St. Paul. It is, so to speak, the theme of his teaching. (14)

As a Doctor of the Church, Augustine greatly developed the Catholic doctrine of predestination.  The fathers previous to the time of St. Augustine, especially the Greek fathers, often interpreted predestination as meaning the will to give glory after this life. They scarcely spoke of it except by way of exhortation, and then they had in mind the preconceived order of execution in which merits precede glory, whereas as intended by God it happens in the inverse order. (15) In the order of intention God wills the end before the means; that is why He wills to save the good thief to whom He grants the grace of final perseverance. But in the order of execution He gives eternal life as the reward of meritorious acts.  This distinction between intention and execution was only gradually applied to the problem of predestination. At first it was applied obscurely by St. Augustine, and then more and more explicitly by the Scholastic theologians.

Predestination, (16) as is defined by the Church, has not been infrequently met with the heresy of predestinarianism:

The essence of this heretical Predestinarianism (17) may be expressed in these two fundamental propositions which bear to each other the relation of cause and effect:

•   the absolute will of God as the sole cause of the salvation or damnation of the individual, without regard to his merits or demerits;

•   as to the elect, it denies the freedom of the will under the influence of efficacious grace while it puts the reprobate under the necessity of committing sin in consequence of the absence of grace.

The Church’s defense of St. Augustine’s doctrine of gratuitous free will clarifies to us what the Church has persistently taught, first of all against predestinarianism, and then against Calvinism, Bajanism, and Jansenism.

In the fifth century, Lucidus, a priest of the Catholic Church who was accused of having taught predestinarianism or predestination to evil, made a retractation of his teaching in the Council of Arles, which was held in the year 473. His opinion, as formulated by the council, reads as follows: "That Christ the Lord, our Savior, did not die for the salvation of all mankind; . . . that God's foreknowledge forcibly impels man to everlasting death, or that those who are lost, are lost by God's will. . . . Likewise I reject the opinion of one who says that some are destined to everlasting death and others are predestined to everlasting life."(18) In his retraction, Lucidus affirmed that he who is lost could have been saved. (19)

Council of Quierzy (853)

Canon 1 - That God wills in a certain way to save all men

Canon 2 - That there is no such thing as predestination to evil, but that God decreed from all eternity to inflict the penalty of damnation for the sin of final impenitence, a sin which He foresaw and in no way caused but merely permitted.

Canon 3 - Almighty God wills without exception, all men to be saved, though not all are saved. That some are saved, however, is the gift of Him who saves; if some perish, it is the fault of them that perish.

The 3rd Council of Valence (855) insisted more strongly on the gratuity of predestination to eternal life in so far as it is distinct from simple foreknowledge, for this latter also extends to evil. According to the declarations of this council, the least good and the least punishment that is justly inflicted, never occur without a positive and infallible decree from God, and no sin is committed, and nowhere by preference, without His foreknowledge and permission.(20)

Council of Langres (859)

Canon 1 - Whatsoever the Lord pleased He hath done in heaven and on earth. For nothing is done in heaven or on earth, except what He Himself is pleased to do, or justly permits to be done. This means that all good things, whether easy or difficult to accomplish, whether natural or supernatural, come from God, and that sin does not occur, nor in this one rather than in the other, without His divine permission.

Canon 2 - God wills all men to be saved and no one to perish. . . nor after the fall of the first man is it His will forcibly to deprive man of free will.

Canon 3 - That those, however, who are walking in the path of righteousness, may continue to do so and persevere in their innocence, He heals and aids their free will by grace.

Canon 4 - They who go far from God, who is desirous of gathering the children of Jerusalem that wills it not, will perish.

Canon 5 - Hence it is because of God's grace that the world is saved; and it is because man has free will that the world be judged.

Canon 6 - Adam, through willing what is evil, lost the power to do what is good. . . . Wherefore the whole human race became a mass of perdition. If no one had been rescued from it, God's justice would not have been to blame. That many are saved, however, is due to God's ineffable grace.

This last statement echoes what St. Augustine said. Thus at the end of these conferences of the ninth century, the bishops, assembled in council at Thuzey, rejected absolutely the theory of predestination to evil and affirmed God's universal will to save, as Prosper had done. God never commands the impossible, but He wills to make it possible for all to fulfil His precepts and obtain salvation. That is what all the bishops assembled in this last mentioned council affirmed with SS. Augustine and Prosper. But they do not deny the other aspect of the mystery, which is: the absolute gratuity of predestination, of true predestination as opposed to reprobation.

In the sixteenth and seventeenth centuries, this teaching of the Church was confirmed both by the decisions of the Council of Trent against the errors of Protestantism and by the condemnation of Jansenism. The Church again declares that man, though having contracted the stain of original sin, is free to do good by the aid of grace, consenting to co-operate with it, though at the same time he can resist it.(21) From this it follows that God predestines no one to evil;(22) but He wills, on the contrary, the salvation of all men; and Christ dies for all, although all do not receive the benefit that is the fruit of His death, "but only those to whom the merit of His passion is communicated."(23) In the case of adults good works are necessary for salvation, and, in the order of execution, heavenly glory is the reward granted at the end of their probation for meritorious acts.

It is likewise declared against Jansenism that Christ did not die only for the predestined, or only for the faithful; (24) that there is a grace which is truly sufficient, and which makes the fulfilment of God's precepts possible for all those on whom these precepts are imposed. The Church, quoting the words of St. Augustine, says again in refuting the Protestants and Jansenists: "God commands not impossibilities, but, by commanding, both admonishes thee to do what thou art able, and to pray for what thou art not able to do."(25) She also says that "God does not abandon the just without previously having been abandoned by them. That some perish, is the fault of those who perish." (26)

Holy Scripture expressed the same thought in these words: "Destruction is thy own, O Israel; thy help is only in Me."(27)

De dono persever., chap. 14.
De praed. sanct., chap. 10.
John 10: 27-28.
Cf. Enchiridion, chap. 100, no. 26
Phil. 2: 13; cf. De praed. sanct., XVIII, 41; De dono persever., XXIII, 63.
De dono persever., XVII, 41, 47; XIX, 48; XX, 50; De praed. sanct., XVII, 34; XVIII, 37.
Cf. Enchiridion, chaps. 95 ff
De correptione et gratia, chap. 14.
Ibid., cf. De civitate Dei, V, 9.
De gratia et libero arbitrio, chap. 16.
De praed. Sanct., chap. 8. In his tractae ad Simplicandum, Bk. I, q.2, no. 13, St. Augustine speaks of a congruent grace that is adapted to the dispositions of the individual, these being known by God
De dono persever., chap.9
In Joan., tr. 26
De dono persever., VIII, 17; IX, 12, 21; XI, 25; XII, 30. De praed. sanct., VIII, 16; XIV, 26. De correptione et gratia, VIII, 17, 19(in the order of execution).
Cf. Dict. de Théol. Cath., art. "Prédestination," by Father Simonin, O.P.
http://www.newadvent.org/cathen/12378a.htm
http://www.newadvent.org/cathen/12376b.htm
http://www.catecheticsonline.com/SourcesofDogma.php,  no. 316
http://www.newadvent.org/cathen/13703a.htm
http://www.catecheticsonline.com/SourcesofDogma.php,  nos. 321-22.
Ibid., no. 797; d. no. 816
Ibid., no. 827.
Ibid., no. 795.
Ibid., nos. 1096, 1294, 1380 ff.
Ibid., no. 804.
Ibid., nos. 804. 806, 1794.
Hosea 13:9


Psalm 22:16-18 reads as follows:

For dogs have surrounded me;
A band of evildoers has encompassed me;
They pierced my hands and my feet.
I can count all my bones.
They look, they stare at me;
They divide my garments among them,
And for my clothing they cast lots.

Here is the New Testament fulfillment of the prophecy in Psalm 22:

Then the soldiers, when they had crucified Jesus, took His outer garments and made four parts, a part to every soldier and also the tunic [Gk chiton]; now the tunic was seamless, woven in one piece. So they said to one another, “Let us not tear it, but cast lots for it, to decide whose it shall be”; this was to fulfill the Scripture:
“They divided My outer garments among them, and for My clothing they cast lots” [John evidently quoted the Greek translation of the Hebrew Scriptures, the Septuagint, or LXX].
Therefore the soldiers did these things.

According to a number of sources, the chiton (χιτών, citwn), which was a long garment worn next to the skin and under the outer cloak, was more expensive to make than an undergarment of several pieces sewn together. Perhaps a seamless chiton looked more presentable than one which was made from piecework. The salient fact in the crucifixion narrative, however, is that since the chiton was seamless, the quaternion of soldiers was reluctant to rip the garment into four pieces (which would spoil the garment) but chose rather to "cast lots" (our equivalent today of throwing dice) to see which soldier would get it whole.
As the writer of the article "The Seamless Tunic" observed:

This prophecy […] declares the commonness of divine prophecy. It shows the characteristic of earthliness that is sometimes present in the fulfillment of God’s predictions. Often He chooses the everyday deeds, the unplanned and common activities of people, as the setting and events through which His prophecies come to pass. These soldiers—having no idea that they were part of God’s designs—went about their normal work of implementing an execution. What they did was routine to them. Perhaps they joked about who got what as they divided the outer garments. When they came to the seamless undergarment, they paused to recognize its beauty; beyond that, it was business as usual. After deciding on what to do with the tunic, they gambled over it and gave it to the winner. These men were unaware that they were fulfilling a prophecy made perhaps a thousand years before. They did not know that their actions had been written into the divine record by David or that they were proving that God overrules in all things to fulfill His will.

While the seamless tunic could be considered a "luxury item" in Jesus's day, Jesus did not possess any other luxury items, particularly toward the end of his public ministry. Here is what he said to a wannabe follower:

"The foxes have holes, and the birds of the air have nests; but the Son of man hath not where to lay his head" (Matthew 8:20; cf. Luke 19:28 KJV).

Perhaps earlier in his life, Jesus may actually have owned a house in Capernaum. Here is what Gospel writer Mark tells us,

καὶ γίνεται κατακεῖσθαι αὐτὸν ἐν τῇ οἰκίᾳ αὐτοῦ καὶ πολλοὶ τελῶναι καὶ ἁμαρτωλοὶ συνανέκειντο τῷ Ἰησοῦ καὶ τοῖς μαθηταῖς αὐτοῦ ἦσαν γὰρ πολλοὶ καὶ ἠκολούθουν αὐτῷ
And it happened that he was reclining in his house, and many tax collectors and sinners were reclining with Jesus and his disciples, for there were many who were following him . . ..

As his public ministry became more and more itinerate, however, he may simply have divested himself of all earthly goods, save for the "clothes on his back," so he could travel light, as it were.
And from Professor Mark Goodacre's blog comes the following,

This may be an example of . . . accidental information, or material given away in passing, where a piece of data (here: Jesus had a house in Capernaum) is assumed and not narrated.

Furthermore, Jesus' basic needs were provided for out of the common pot, of which Judas Iscariot was in charge (see John 12:6), and a number of prominent women contributed to his support as well (Luke 8:2-3).
The apostle Paul also reminds us:

For ye know the grace of our Lord Jesus Christ, that, though he was rich, yet for your sakes he became poor, that ye through his poverty might be rich (2 Corinthians 8:9 KJV).

All the above is to say: While Jesus may have owned a tailor-made tunic, it may have been made by his mother or by another talented (perhaps wealthy) seamstress who may have been a follower of our Lord. Obviously, Jesus did not live in the lap of luxury. Moreover, he was content to entrust the moneybag to a thief, which as writer Jon Bloom observes,

Of all the disciples, Jesus chose Judas to be treasurer of his itinerant nonprofit. One is tempted to offer the Lord some consulting on good stewardship. Donors were financially supporting this ministry (Luke 8:3) and the one guy who Jesus knew was a “devil” (John 6:70) was made CFO.
Now, Jesus was not ignorant of Judas’s pilfering. So why did he let him manage the money?
I believe Jesus was putting his money where his mouth was.
He said, “Do not lay up for yourselves treasures on earth, where. . . thieves break in and steal” (Matthew 6:19-20). So he showed us by example what he meant.