In the OT era (before Christ and His church), believers were told to teach in the following way:
Psalm 78 (ESV, and note that these same directions occur many times in the Old Testament):
1 Give ear, O my people, to my teaching; incline your ears to the words of my mouth!
2 I will open my mouth in a parable; I will utter dark sayings from of old,
3 things that we have heard and known, that our fathers have told us.
4 We will not hide them from their children, but tell to the coming generation the glorious deeds of the LORD, and his might, and the wonders that he has done.
5 He established a testimony in Jacob and appointed a law in Israel, which he commanded our fathers to teach to their children,
6 that the next generation might know them, the children yet unborn, and arise and tell them to their children,
7 so that they should set their hope in God and not forget the works of God, but keep his commandments;
8 and that they should not be like their fathers, a stubborn and rebellious generation, a generation whose heart was not steadfast, whose spirit was not faithful to God.
In other words, back then teaching was intended to preserve the knowledge of God from one generation to the next, and show each generation both the mighty works of God, and also His commandments, so that every generation would know and do God's will.
In the present, teaching about God is meant to be twofold in purpose:
1. It includes what's in the Old Testament teaching prescription;
2. It advances to communicating the truth to everyone, the world over.
(Matthew 28, Mark 16, Luke 24, John 20, Acts 1, Romans 1, etc.)
18 And Jesus came and said to them, "All authority in heaven and on earth has been given to me.
19 Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit,
20 teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age."
15 And he said to them, "Go into all the world and proclaim the gospel to the whole creation.
16 Whoever believes and is baptized will be saved, but whoever does not believe will be condemned.
46 and [Jesus] said to them, "Thus it is written, that the Christ should suffer and on the third day rise from the dead,
47 and that repentance and forgiveness of sins should be proclaimed in his name to all nations, beginning from Jerusalem.
30 Now Jesus did many other signs in the presence of the disciples, which are not written in this book;
31 but these are written so that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name.
8 [Jesus said] you will receive power when the Holy Spirit has come upon you, and you will be my witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth."
16 For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek.
So for the Old Testament, heads of households, priests, and other teachers were told, "Teach the people of God His works, knowing Him, and His commandments and directions.
In the New Testament, the disciples of Jesus are told, "Teach everyone the Gospel."
Churches in our era are pretty good at teaching the Bible. Some don't, of course, but for the most part, if a church and minister believe the Bible, they do teach it, so that the next generation may know God and do His will.
However, churches are really pretty terrible at communicating the Gospel to "all nations," "all creation," and "everyone."
So as ministers, members of churches, and individual Christians, I believe God says this to us:
"Teach the people IN church how to know and follow Me."
"Teach the people OUTSIDE the church how to believe in Me and follow Me."
"Teach the people OUTSIDE the church why they must believe in Me and follow Me."
This is our greatest failure. We must go. We must go. We MUST go.
It is great that our churches teach the truth, and also teach the Gospel, but we must GO.
An interesting fact:
The last few people I have personally led to Christ, I led to Him AT church, AFTER church. The church did get them there, but it was the personal touch that brought them to Him. It's the same with you. You can reach people nobody else can, because you are in contact with them, and they are your friends. You don't have to do as much as you think. I remember my brother came to Christ, many years ago, because I wouldn't let him alone. I kept bugging him. And then he wouldn't tell me (he was my brother, after all).
Talk to your friends. Don't buttonhole them, just talk to them. Be their friend, and not just their "converter;" in other words, make friends, don't pretend to make friends in order to convert them. People see through this rather easily, and they definitely dislike it.
You will touch many lives just by being a friend and then telling your friends about Christ (how He gives them strength in difficulty, for example, or comforts in tragedy, or gives eternal life to the dying). You don't need to give them all the doctrine, just tell them briefly.
Invite them to believe with you.
You WILL touch many lives.
AND you will make the Lord really happy.