According to the Bible
The book of Acts
The Book of Acts records or reports that there was a special event that took place at Pentecost, which would have been the next pilgrimage festival after the Passover at which Jesus died. And at that time the disciples of Jesus were gathered together in Jerusalem unsure of what their future would be, when all of a sudden the spirit took hold of them and enabled them to speak in tongues, and that speaking of tongues is understood by the author of the Book of Acts to mean speaking in all of the languages of the world. So with the power of the spirit behind them, the disciples of Jesus immediately began a missionary campaign and started bringing people into Christianity, converting them to belief in Christ. And from that time forward the mission moved ahead in the rather smooth way, directed by the spirit and by all of the apostles. This is the picture that we get in the book of Acts.
Christianity compared to other religions.
Types of Christianity.
There were very different views of Jesus in the various types of Christianity. Perhaps the starkest contrast was among those who considered themselves as gnostic Christians, and those who considered themselves Christians in the old Pauline view of things. On the one hand, Paul, and Pauline Christianity, would have placed all of the emphasis on Jesus' death and resurrection, and the saving power of that death and resurrection. Gnostic Christianity, on the other hand, would have placed its prime emphasis on the message, the wisdom, the knowledge, the gnosis, that's where the word gnostic comes from, the Greek word for knowledge, the knowledge that Jesus transmits, and even the secret knowledge that Jesus transmits. So one would have on the one hand faith in the saving event of Jesus' life and death, and on the other hand knowledge as the great source of adherence to the Jesus movement on the other hand.
Diversity in early Christianty
Christianity did not start out as a unified movement. We have to remember that the disciples left early and at many different times. That is, at a time where there was no fixed "rules"on what the Christian beliefs should be. What Christian rituals should be. What they should think about Jesus or what they should preach about Jesus.
With a explosive spread of Christian churches, not a slow growth, but an explosive spread of this movement, it cannot be expected that everywhere, everybody was doing and believing the same thing, singing the same hymns and reading the same scriptures and telling the same story. So we begin with a great diversity.in the second century we begin to establish a greater unity among the diverse churches. This unifying process is already happening in Pauls churches because Paul writes letters to all of them to see,understand, and check on them.