The primitive church was split - Paul (from the Diaspora and unknown in Jerusalem - he says so) was based in Antioch while the group at Jerusalem, headed by James, Peter and John, focused on the Jews. Indeed, the Jerusalem Church saw themselves as part of Judaism.
The Jerusalem Church morphed into the Ebionites whereas Paul's sect ultimately gained the political ascendancy, helped along in no small measure by the Roman emperors. The majority of the Christian Scriptures come from Paul or from his disciples, because they were selected - fundamentally from the 2nd century on but dominantly from the 4th to 7th centuries - by those whose allegiance was to Paul, not to the other sects, such as the Ebionites or with Marcion, for example.
The sequence of the letters attributed by Paul is dictated by their length. Scholars say that only 7 of the letters attributed to Paul were actually by him. Many of those those that were by Paul is a collection of several letters, stitched together to make them appear as it was a single letter.
As with any part of the Scriptures, the writer was concerned with his own immediate time, with his own immediate community, trying to influence them, using idioms, terminology, and illustrations that had meaning to them at that time, according to their cultures.
Even the epistles attributed to Peter were written by a follower of Paul -- 2 Peter was written about 100 years after Peter's and Paul's deaths.
http://www.jwstudies.com/2013_-_Did_a__Governing_Body__govern_Paul.pdf
http://www.jwstudies.com/The_Watchtower_s_Achilles__Heel.pdf
http://www.jwstudies.com/Why_Does_WTS_Accept_Christendoms_Scriptures.pdf
Doug