The Historical Roots Of The Gospel Canon

One of the best books I've read on the historical origins of the four-gospel canon is C.E. Hill's Who Chose The Gospels? (New York: Oxford University Press, 2010). I want to quote some portions of it, though what I'm about to quote only represents a small portion of the evidence Hill discusses:

In the last two or three decades of the second century Irenaeus in Gaul, Clement in Alexandria, Theophilus and Serapion in Antioch, and the author of the Muratorian Fragment in or near Rome, at points far distant from each another on the map, are all saying or implying that the church has the same four acknowledged Gospels….

It is thus not without reason that Perkins sees the Apocryphon of James [an anti-orthodox heretical document written in the early to mid second century] as an example 'of the growing influence of the canonical Gospels'. It assumes the previous acceptance of probably all four of these Gospels and does not contest the tradition that they go ultimately back to Jesus' original disciples. It simply treats those Gospels as inadequate….

And not to be forgotten is the fact that opponents of 'apostolic Christianity' generally conceded that its faith was indeed 'apostolic'. 'The Gospel of Judas', for instance, writes DeConick, 'attempts to harpoon apostolic Christianity for its blind reliance on the authority of the twelve apostles for its teachings.' Nor did opponents typically dispute even the idea that the four Gospels ultimately went back to the apostles of Jesus. As we saw in Chapters 7 and 8, some of the most striking testimony on behalf of the four Gospels, and other parts of the New Testament, comes from outside of apostolic Christianity. Most, if not all, of the known rival Gospels, and other pseudepigraphical works as well, actually presuppose to one extent or another the witness of the canonical Gospels. Pagan critics of Christianity like Celsus, when they took the time to read the Christian sources, went to the same canonical Gospels, which Celsus, at least, accepted as written by Jesus' disciples….

But by and large, the apostles of Jesus could simply be treated [by heretics] as spiritual novices, or something much less complimentary. For the highest appeal among such groups as these was typically to a professed 'secret knowledge', superior to the commonly received, public teaching of the apostles (cf. Irenaeus, AH 3.2.1). The Gospel of Thomas begins: 'These are the secret sayings that the living Jesus spoke and Didymos Judas Thomas recorded.' The Gospel of Judas begins: 'The secret revelatory discourse in which Jesus spoke with Judas Iscariot.' The persistent appeal to secret teachings of Jesus given to one or another of the apostles is a tacit admission that not very much support could be gained [for heretical beliefs] from his acknowledged public teachings. (99, 169, 234-235)