What were the guidelines for setting up the New Testament?

Answer 1

The guidelines for canonising the books that now form the New Testament were firstly to select those books that were believed to really have been written by the early apostles and secondly those books that most closely matched the theology of the dominant Church at that time.

The first to use the term "New Testament" was Irenaeus, who was assistant to the first bishop of Lyon (France) and flourished about 180 CE. He called for four gospels, and exactly four, on the basis that there were four corners of the world and four winds. Those Gospels, he said, were to be those of Matthew, Mark, Luke and John.Thus, the Gospel of Thomas was excluded, as were many other gospels, mainly from the Gnostic branch of early Christianity.

The epistles attributed to St Paul were probably an automatic choice. Hebrews was not a widely read book, but was preserved and included in the New Testament because, at the time, it was also attributed to Paul. The claim to include Revelation was strongly disputed, but the view, that "John of Patmos" was the same John as mentioned by the gospels, won the day.