The authentic teaching of the Church about Jesus began, not as a book, but as an oral tradition — preached and passed on by the apostles and others who knew him personally (see “Why Are There Four Gospels?”). Once the faith had spread throughout the Roman world and beyond, portions of this oral tradition were committed to writing and circulated among the scattered local churches. The resulting books were recognized by these churches as reliable and authoritative accounts because they judged them to be in keeping with, and rooted in, the genuine apostolic Tradition they already possessed.
Three criteria were used to evaluate a book for which a claim to divine inspiration had been made: First, was it written by an apostle or an associate of an apostle? Second, did it conform to the “rule of faith,” the doctrinal Tradition, affirmed by churches throughout the world? Third, had it been read publicly and regularly in Christian worship, especially in those churches with apostolic beginnings?
Writings from the generations of Christians just after the apostles show that they quoted as authoritative the four gospels we now have in our Bibles. By the mid-second century, teachers living as far apart as St. Ignatius in Syria, St. Justin Martyr in Rome, Tertullian in Africa, and St. Irenaeus in what is now France had all accepted as reliable and divinely inspired the gospels of Matthew, Mark, Luke, and John. This judgment was later confirmed authoritatively by formal Church councils, but certainly not by a Roman imperial decree.
A few other ancient writers did indeed claim to tell about Jesus’ life; St. Luke himself noted some of them (see Lk 1:1). But their books were not “banned” by the “hierarchy.” Rather, they never gained acceptance by the Church as a whole in the first place because they failed to meet the reasonable criteria described above. Books such as the “Gospel of Thomas” were thus rejected as later products of eccentric teachers. The genuine apostolic Tradition exposed them as a false “different gospel” (see Gal 1:6-9).