Why were books not included in the New Testament Canon?

A:

The choice of what books to include in the New Testament was partly a political decision and partly based on which books were thought to have been written by the apostles or associates of apostles. The decision as to whether a book was really written by the apostles or associates of apostles was, in turn, based on whether the Church Fathers agreed with the theology of the book.

On the one hand, we have books such as 1 Peter and Jude included in the canon in spite of strong opposition. On the other hand, for example, the Gospel of Thomas was excluded in spite of strong support. 3 Corinthians, one of the pseudo-Pauline epistles was excluded, yet Ephesians, Colossians, 2 Thessalonians, 1 Timothy, 2 Timothy and Titus were included.

The Apocalypse of Peter nearly made into into the New Testament, but was finally excluded. The Revelation of John was widely thought to be spurious, yet was accepted into the canon because the author signed himself as John and some of the Church Fathers thought that this was probably the apostle John.