Christianity comprises a group of religious traditions originating with Jesus Christ which generally assert that Jesus is the son of God, and the messiah: the sole savior of all humanity. That is, Jesus redeemed mankind from their sins (i.e. faults, misdeeds, rebellion against God), reconciling mankind to God so that man can live eternally with God in a state of never-ending happiness.
Christianity emerged from Judaism in the first century of the common era. Christians brought from Judaism its scriptures; fundamental doctrines such as monotheism; the belief in a moshiach (Hebrew term for messiah); this term is more commonly known as Christ (christos in Greek) and means 'the annointed one'; form of worship, including a priesthood, concepts of sacred space and sacred time, the idea that worship here on Earth is patterned after worship in Heaven, and the use of the Psalms in community prayer. The book of Acts says that Christ's followers were first called Christians by non-believers in the city of Antioch, were they had fled to and settled after early persecutions in Palestine, probably just a few years after Jesus' resurrection and ascension.
The Jewish picture of the messiah is a national, more or less political one - they expected the deliverer of Israel, the Davidic king who'se reign would never end. This promise was first uttered by the prophet Samuel, and repeated in different wording by most of the Jewish prophets after him. The Jewish picture of the messiah has significant differences from how Christians understand the term. They usually adhere to what Christ himself said about his mission (as written in the Bible): (a) he was the fulfillment of at least some of these Old Testament prophecies, (b) he came to establish the Kingdom of God (or Kingdom of Heaven) which was not to be an earthly kingdom, (c) when asked straight in the face whether he was the expected messiah, he pointed at the miracles he performed and (d) by demonstratively washing the disciples' feet he pictured himself to be a 'servant-king'.
The most crucial points in Christian teaching are Jesus' incarnation, crucifixion and death, and his miraculous resurrection. These events are believed by Christians to be the basis of God's work to reconcile humanity with himself. Most Christian groups believe Jesus to be God (ie: incarnated as both fully human and divine), although there has been never-ending dispute over in what way he is God (see Christology). A few Christian groups (Arians, Jehovah's Witnesses, Unification Church) have denied that he is God, saying instead that he is a created being second only to God. Some gnostic Christians argued that he was fully God, but only seemed to be fully human. In a few more liberal sects, Jesus is not believed to be God, but rather is viewed simply as someone who had new insights and something to teach. The stated doctrines of Catholic, Orthodox, and Protestant churches hold that Jesus was both fully God and fully man, and hold this to be an essential element of the faith.
Christians believe the Bible is the word of God to some degree or another. Even though Christians disagree about how accurate the Bible is and how it should be interpreted, the Bible is still the most widely regarded source of information about Jesus. It maintains that Jesus is the messiah which the Jews have long awaited; thus Christianity could be considered (at least by Christians) to be the continuation or fulfillment of the Jewish faith. Christians and Jews both consider the Old Testament (what Jews call the Tanakh) to be the word of God. Some christians include additional books, but most agree on which books comprise the Old Testament (see biblical canon). The New Testament is the second part of the Christian Bible, containing accounts of the life of Jesus, the earliest church, and a number of epistles (letters) written by some of the Apostles to various audiences. Very few Christians include extra books beyond the 27 generally accepted.
The greatest division in Christianity is between the eastern and western branches. The Western branch developed in the Western Roman Empire, while the Eastern branch developed in the Eastern Roman Empire. The Western branch is divided principally into Catholicism and Protestantism, while the two main divisions of the Eastern branch are Eastern Orthodoxy and Oriental Orthodoxy. See the Great Schism for the history and circumstances of this division.
= Western branches
Catholicism and Protestantism are the two major divisions of Christianity in the Western world (Western Europe and the Americas). For example, the Baptist, Methodist, and Lutheran churches are generally considered to be Protestant faiths, although strictly speaking, of these three the Lutheran denomination is the only one of these founded as a "protest" against Catholicism. The Anglican (Church of England) is generally classified as Protestant, but it is properly understood as its own tradition—a via media ("middle way") between the Protestant and Catholic traditions.
One central tenet of Catholicism is its literal adherence to apostolic succession. "Apostle" means "one who is sent out." Jesus commissioned the first twelve apostles (see Biblical Figures for the list of the Twelve), and they, in turn laid hands on subsequent church leaders to ordain (commission) them for ministry. In this manner, Catholics can trace their ordained ministers all the way back to the original Twelve. Roman Catholics are distinct in their belief that the Pope has authority which can be traced directly to the apostle Peter. Other Catholic groupings include the Old Catholic Church which rejected the definition of papal infallibility at the First Vatican Council, and Anglo-Catholics, Anglicans who believe that Anglicanism is a continuation of historical Catholicism and who incorporate many Catholic beliefs and practices.
Protestant faiths trace their roots to the work of Martin Luther and John Calvin, who believed that the Catholic church had deviated too far from the practices and beliefs of the original churches described in the New Testament. They attempted to reform the Catholic Church but failed. The protestant reformation resulted instead. Protestantism as a whole has never been led by a pope or other institution having such an over-all authority. Each protestant movement has developed freely, and many have split over theological issues. That is how over the centuries it has developed into a great number of independent denominations. A number of movements that grew out of spiritual revivals, like Methodism and Pentecostalism, also consider themselves Protestant. The measure of mutual acceptance between the denomonations and movements varies, but is growing. Protestant theology for each denomination is usually guarded by church councils.
In the Eastern world (Eastern Europe, Asia) the primary representative of Christianity is Eastern Orthodoxy. The Eastern Orthodox Church also believes it is the continuation of the original Christian church established by Christ. Originally there were five main centers of Christianity in the ancient world: Rome, Constantinople, Alexandria, Antioch, and Jerusalem. According to the Eastern Churches' understanding of Papal primacy, the bishop of Rome was first in honor among the bishops, but possessed no direct authority over dioceses other than his own. In the Great Schism, conventionally dated to 1054, the Eastern Churches severed communion with Rome over a number of issues centered around the differing understanding of Papal primacy. The four other Churches remained in communion with each other and still exist today along with less prestigious, but often more populous, self-governing or "autocephalous" Churches organized more or less along national lines. The largest of these, and the largest Orthodox Church overall, is the Church of Russia. Many of these groups are represented as independent ecclesiastical bodies in America. There exist significant theological differences between the Orthodox Church and Western Christianity.
The Eastern Orthodox Churches accepted the Chalcedonian dogma on the nature of Christ, which was also accepted by the Western branch of the church; while the Oriental Orthodox rejected it. The Oriental Orthodox comprise chiefly the Monophysites (e.g. the Coptic church or the Syrian Jacobites) and the Nestorians (e.g. the Assyrian Church).
Several other faiths, which also believe in Jesus Christ, claim not to be descended from any of these groups directly. The Church of Jesus Christ of Latter-Day Saints, for instance, is often grouped with Protestant religions, but disagrees with this classification.
Many people belonging to the above-listed groups have strong feelings about the legitimacy of the other Christian faiths, sometimes even claiming that the other faiths do not actually count as Christian. These claims usually rely on more specialized definitions of "Christianity" than an outsider might assume, entailing points of doctrine which are critical to the objecting faith's view, such as belief in the doctrine of the Holy Trinity (an agreement on the nature of God the Father, Jesus Christ, and the Holy Spirit reached in A.D. 325) or the doctrine called "Biblical inerrancy" (a specific set of beliefs regarding the nature of the Bible). Catholics and Protestants in particular may consider these beliefs critical to "real" Christianity, and may thus exclude churches such as The Church of Jesus Christ of Latter-day Saints, the Jehovah's Witnesses and the Unification Church who differ on these views (but feature Jesus Christ as a central part of their belief system, and consider themselves Christian). Others, such as Unitarian-Universalists, consider themselves as borderline Christians, since Jesus Christ is not pivotal to their belief system.
In adition Christianity, has inspired other religions whose adherents do not consider themselves Christians but do consider Jesus to be a prophet. Islam is the most sucessful of these.
The following ASCII art diagram shows the historical development of traditional Christian groups:
/--------------Protestantism Reformation ----------------> / [[/Western]] Church----------------Roman Catholicism (Western Rites) / /---Roman Catholicism (Eastern Rites) Early / Great Schism / Christianity ....................=======/================ / \ Eastern Orthodoxy \ / \Eastern Church Chalcedonian -----> \ Controversies \--Nestorians ) Oriental \---Monophysites ) Orthodox
Not all people who identify as Christians accept all, or even most, of the theological positions that their particular church mandates. Like the Jewish people, Christians in the West were greatly affected by The Enlightenment in the late 17th and early 18th centuries. Perhaps the most significant change for them was total or effective separation of Church and State, thus ending the state-sponsored Christianity that existed in so many European countries. Now one could be a free member of society and disagree with one's church on various issues, and one could even be free to leave the church altogether. Millions did take these paths, becoming freethinkers and developing entirely new belief systems such as humanism, atheism, agnosticism, and deism; others created liberal wings of Protestant Christian theology, and the long-suppressed Unitarian trend in Christitianity became an acceptable choice for many. The Enlightenment had a much less profound impact on the Eastern Churches of Eastern and Oriental Orthodoxy.
This gain in personal freedom came with a social price: the dissolution of the Christian community as an entity with civic legal authority. In the United States and Europe, many secularized Christians have long since stopped participating in traditional religious duties, attending churches only on holy days or not at all. Many of them recall having highly religious grandparents, but grew up in homes where Christian theology was no longer a priority. They have developed ambivalent feelings towards their religious duties. On the one hand they cling to their traditions for identity reasons; on the other hand, the influence of the secular Western mentality, the demands of daily life, and peer pressure tear them away from traditional Christianity. Marriage between Christians of different denominations, or between a Christian and a non-Christian, was once taboo, but has become commonplace.
There have been many responses to this phenomenon within the Christian community, including the development of literally thousands of Christian Protestant denominations, traditionalist splinter groups of the Catholic Church that do not recognize the legitimacy of many reforms the church has undertaken, and fundamentalist groups that interpret the entire Bible as literal truth.
For the full history of Christianity, see the article so titled.
Non-Protestant, non-Catholic Christianity: The Church of Jesus Christ of Latter-Day Saints -- Jehovah's Witnesses -- Unification Church -- Religious Society of Friends (Quakers) -- Church of Christ, Scientist (Christian Scientists) -- Sons Aumen Israel -- Unity Church
Unitarian Universalism is not a creedal religion, and espouses no official spiritual beliefs. Unitarian Universalists see themselves as a liberal religious community where people of differing beliefs share with each other and learn from each other. Before the 20th century, the church was much more Christian, but it has become increasingly diverse.
Links to integrate with the above (taken from religion): Anglicanism (Episcopal) -- Lutheranism -- Presbyterianism -- Calvinism -- Baptist Church -- Evangelical -- Church of Christ -- Methodist Church -- Pentecostals -- Charismatics and many more.
A summary of Christian views of homosexuality is available..
Relevant books: The Rise of Christianity (book by Rodney Stark)