From "Misquoting Jesus" 2

An idea from “Misquoting Jesus” contends that scholars have long suspected that some of the letters in the New Testament attributed to Apostles were actually written pseudonymously by second generation followers of those men.

The writing of letters as a means of instruction was very important in the early Christian Church. Letters were copied and sent out to surrounding congregations. They helped make Christianity quite different from the other religions scattered around the Roman Empire. The scattered Christian communities were united by these letters, unified in a common literature.