David Brakke has published a signifcant essay with a fresh translation of Athanasius’s Thirty-Ninth Festal Letter:
“A New Fragment of Athanasius’s 39th Festal Letter: Heresy, Apocrypha, and the Canon.” Harvard Theological Review 103 (2010): 47-66.
He points to some of the implications of a “new fragment of the Coptic text” of Athanasius’s Thirty-Ninth Festal Letter:
“When I read the letter in the mid 1990s, I argued that Athanasius’s promotion of a biblical canon supported a parish-based, episcopally-centered spirituality in opposition to other forms of Christian authority, namely, the teacher and the martyr. I still think that is the case, but the new fragment does suggest that I underestimated the specifically anti-heretical intent of the letter and of Athanasius’s canon. That is, Athanasius promoted a biblical canon not only—as I argued earlier—to support one form of Christian piety, social formation, and authority in opposition to others, but also to refute the specific teachings of persons and groups that he deemed ‘impious’ and ‘heretics.’”
As for what’s new in the new fragment:
“ . . . . These other passages do not, however, include brief descriptions of each heresy’s distinct false teaching as the new fragment does.”
“While the beginning and end of the fragment merely extend or supplement what we already knew of Athanasius’s argument, the brief catalogue of heresies with the biblical passages that refute them in its central section is genuinely new . . .”
Brakke makes an observation that supports the notion that the early church rejected pseudepigraphy/pseudonymity, writing of Athanasius:
“. . . he devotes considerable attention to two particular themes. . . . The second theme is that no ‘apocryphal’ books really come from Isaiah, Moses, Enoch, or any other authoritative figure. They all published their teaching openly, and any ‘apocryphal’ books attributed to them must be recent inventions of heretics.”
This comment adds to a lot of other evidence that when early figures in the church wrongly cited extra-canonical books as Scripture, they did so thinking that the attribution to some ancient inspired prophet was genuine. In other words, had they known the document was pseudepigraphical or pseudonymous, they would have rejected it. To my thinking this adds to the evidence that there were clear notions of authorship in the ancient world, that Jesus accepted the traditional claims about who wrote the books of the OT (e.g., Moses wrote the Pentateuch, Isaiah wrote Isaiah, Daniel wrote Daniel, etc.), and that the early church followed Jesus on this point.
Athanasius’s Thirty-Ninth Festal Letter is not saying something new about the canon. Rather, Athanasius sees himself re-stating ancient tradition. Brakke writes:
“As Athanasius and others like him present the matter, when legitimate officeholders of the church (bishops) teach, they are faithfully passing on what Christ told the disciples, who subsequently informed their Episcopal successors, and so they are not really teaching at all. Athanasius claims this about himself in our letter: ‘I have not written these things as if I were teaching, for I have not attained such a rank. . . . I thus have informed you of everything that I heard from my father,’ that is, Bishop Alexander of Alexandria.”
Athanasius was a shepherd seeking to protect the flock from wolves:
“Although most scholars remain focused on the lists of books, the greater importance of the letter is that it reveals the role of canon formation in supporting one form of Christian piety and authority and undermining others. . . . The new fragment . . . makes clear that in establishing a defined canon Athanasius sought to undermine not only a general spirituality of free intellectual inquiry and its academic mode of authority, but also the specific false doctrines to which he believed such a spirituality gave rise.”
A fresh translation of the entire letter, with a revised version of the new Coptic Fragment, follows on pages 57–66.
 David Brakke, “A New Fragment of Athanasius‘s Thirty-Ninth Festal Letter: Heresy, Apocrypha, and the Canon,” Harvard Theological Review 103 (2010): 48.
 Ibid., 50.
 Ibid., 51.
 Ibid., 53.
 Ibid., 56.