... Rather than focusing primarily on ‘the four gospels’, perhaps with just a passing mention of non-canonical texts or text-fragments such as the Gospel of Thomas, the Gospel of Peter, or the Egerton Gospel, we might envisage a broader object of study, that of early Christian gospel literature viewed as a single though differentiated field. Framed in this way, the fourfold canonical gospel would be seen to emerge out of a more extensive literary activity in which traditions about Jesus’ earthly life and teaching were shaped and created—presumably in response to popular demand for gospel-like works from a burgeoning Christian reading-and-listening public ...
... the distinction between canonical and non-canonical gospels is relative to the communities in which they are regarded as such.
Connecting Gospels: Beyond the Canonical/Non-Canonical Divide (Kindle Locations 253-258, 276). OUP Oxford, 2018.
The first chapter titled Praeparatio Evangelica in Early Christian Gospels' is by Simon Gathercole -
Some early Christian texts make extensive reference to scripture, including the canonical Gospels, GPeter and GEgerton. Other works appeal to additional sources: the Apocryphon of John refers to the Book of Zoroaster (Ap. John II 19.10) while the Exegesis on the Soul cites and explores Homer (Exeg. Soul II 136.16–137.11) ...
... GTruth was clearly known as such to Irenaeus (even while he remarks on its difference from the canonical Gospels), and this work is very likely to be substantially the same as Nag Hammadi I,3. ... the title ‘the Egyptian Gospel’ (or Gospel of the Egyptians) must be considered to be one of the titles of NHC III,2 and IV,2 alongside The Holy Book of the Great Invisible Spirit. This should occasion no surprise, given that double-titles were very common in antiquity: Diogenes Laertius, for example, gives double-titles for almost all of Plato’s dialogues, while other authors refer to the same work variously as the Phaedo (Aristotle, Celsus, Clement) or the Peri Psuchēs (Galen, Sextus Empiricus, Clement again). Although GEgyptians is often referred to as the ‘so-called’ Gospel of the Egyptians, Hedrick may well be correct that the Gospel title included in the colophon in Codex III attests to the fact that ‘the document is “gospel” in the sense of the proclamation of the early church’.
THE GOSPEL OF TRUTH
GTruth is a Valentinian work often described as a homily or a meditation, but in reality it is difficult to classify as far as form is concerned. Its subject matter, however, is clearly ‘the good news’, as noted in the opening words (16.31) as well as later: ‘This is the word of the gospel of the discovery of the pleroma, for those who await the salvation which is coming from on high’ (34.34–35.2) ... GTruth focuses on two main elements, Jesus’ revelatory teaching and his suffering. The ‘Word appeared’ and ‘became a body’ ...
... Jesus is further described as ‘the shepherd who left behind the ninety-nine sheep which were not lost. He went searching for the one that had gone astray’ (31.35–32.3). Or again, still in the shepherding imagery: ‘Even on the Sabbath, he laboured for the sheep that he found fallen into the pit’ (32.18–20). Another parabolic section describes the coming of the Word in the incarnation almost as a bull bursting into a china-shop . .
There is a genuine interest in the historical life of this incarnate Word, then: ‘the merciful one, the faithful one, Jesus, was patient in accepting sufferings’ (20.10–11) .... The dominant focus in GTruth is not the earthly ministry but the mythological backdrop to the Gospel history ...
Where does GTruth stand, then, on the question of how the gospel events assume and relate to a past? Is there antecedent revelation which is in some sense fulfilled in what is recounted in GTruth? Negatively, there is no hint of scriptural fulfilment or antecedent textual revelation of any kind. This is not to say that GTruth rejects other texts: it contains dozens of allusions to New Testament writings. As far as the Old Testament is concerned there is just one potential allusion, the passage according to which Jesus ‘was nailed to a tree and became the fruit of the knowledge of the Father’ (18.24–6). Layton reads this passage in light of the Genesis narrative, contrasting the tree of the cross and the tree of the knowledge of good and evil. This interpretation is probable in view of the reference to Jesus as the fruit of the knowledge of the Father on the tree, the fruit that ‘does not bring ruin’, in contrast presumably to the tree of knowledge in Genesis that did (GTr 18.11–33). This may be the tip of an exegetical iceberg, but it is unclear what the particular iceberg might be. A wider discourse about the fall may be presupposed here, expressible in terms other than those expounded in GTruth. Alternatively, there may be a kind of Law/Gospel contrast, and the contrast might even be with an account of the fall which it rejects altogether.
Connecting Gospels: Beyond the Canonical/Non-Canonical Divide (Kindle Locations 541-624). OUP Oxford, 2018.