EOB = Craig Evans and Emanuel Tov, edd., Exploring The Origins Of The Bible (Grand Rapids, Michigan: Baker Academic, 2008)
HVS = Craig Allert, A High View Of Scripture? (Grand Rapids, Michigan: Baker Academic, 2007)
OES = Susan Ashbrook Harvey and David Hunter, edd., The Oxford Handbook Of Early Christian Studies (New York: Oxford University Press, 2008)
TCD = Lee McDonald and James Sanders, edd., The Canon Debate (Peabody, Massachusetts: Hendrickson Publishers, 2002)
In my first post in this series on the New Testament canon, I quoted Craig Allert:
"Athanasius's Festal Letter 39 (367) is recognized as the first document to list our present twenty-seven-book New Testament as 'canonical.'...Further, it is an interesting anomaly that evangelicals generally use Athanasius's New Testament list for support on canonical issues but tend to ignore his Old Testament list, which includes apocryphal books. If he is authoritative for one, why is he not authoritative for the other?" (HVS, 51 and n. 39 on 51)
The testimony of Athanasius on the New Testament canon is one line of evidence among many others. The other evidence relevant to the New Testament canon is much more consistent with Athanasius' conclusion than the other evidence relevant to the Old Testament canon is to his conclusion on that matter.
We've addressed the Old Testament canon many times. Anybody who's interested can consult the archives. The present series of posts is about the New Testament canon. But I'll briefly outline some of the evidence supporting the Evangelical Old Testament.
When discussing the Old Testament canon, people often make much of the issue of how many divisions an ancient source saw within that canon. Did he refer to only two categories, such as "the Law and the Prophets", or did he include a third category, with a title like "the Writings"? However, the grouping of the Old Testament books doesn't have much significance. The books were sometimes placed into two categories, such as "the Law and the Prophets", while including books that would later be commonly classified as part of a third category (EOB, 106-107). Melito of Sardis, for example, as late as the second century A.D., refers to the Old Testament as "the Law and the Prophets" while including books that others would classify as part of "the Writings" (Eusebius, Church History, 4:26). The number of divisions within the canon doesn't tell us much.
Ben Sira, a Jew writing in the second century B.C., comments that his canon is the same as his grandfather's, which is evidence against the sort of canonical instability that many think existed at the time (EOB, 113). In the first century A.D., Josephus claims agreement among the Jewish people for generations regarding their Old Testament canon. Though we know that some Jews disagreed about the canon, and Josephus probably was speaking hyperbolically or dishonestly (or both) when he suggested otherwise, his comments likely at least reflect a majority agreement on the canon. He associates the closing of the canon with a cessation of the succession of prophets, and his comments on such a cessation are self-consistent and corroborated by multiple Jewish sources, some before his time and some shortly after (TCD, 54, 116-117, 119). The early post-apostolic rabbis believed that the canon was closed prior to the writing of the Apocryphal books (TCD, 163-184). Gnostics of the second century seem to recognize the Jewish consensus (TCD, 370). Justin Martyr repeatedly accuses the Jews of his day of altering particular passages within the Old Testament (Dialogue With Trypho, 71-73, 120), but doesn't accuse them of changing the Old Testament canon.
The Roman Catholic scholar Daniel Harrington notes the absence of any convincing evidence that Jesus and the apostles treated any of the Apocryphal books as scripture in the New Testament (TCD, 200-202). Though Jesus and the apostles don't address the issue explicitly or in depth, they seem to have accepted the general Jewish canonical consensus of their day. They don't argue over the contents of the canon, and they sometimes make comments that are best explained under the premise that they agreed with each other and a Jewish consensus on all of the Old Testament (Luke 24:27, Acts 24:14, Romans 3:2). Though many of the Christians of the patristic era accepted one or more of the Apocryphal books, and they sometimes accepted Apocryphal books widely rejected today, like 1 Enoch, some of the patristic Christians rejected all or almost all of those books, such as Melito of Sardis and Jerome. Apparently, a lack of discussion of the Old Testament canon among the earliest Christians, the rejection of the Jewish canonical consensus by a minority of Jews, the gradual distancing of Christians from Jews and Jewish history, and the inclusion of different books in different copies of the Septuagint resulted in a lot of ignorance and disagreement over the Old Testament canon among the patristic Christians.
Jesus and the apostles accepted a Jewish canonical consensus, not a later Christian Old Testament consensus. The early Christians' historical proximity to the New Testament documents, and thus their proximity to historical issues related to the canonicity of those documents, is different from their relationship with the Old Testament. A Christian like Polycarp, Tertullian, or Augustine wasn't in as good a position to judge the Old Testament as he was to judge the New Testament. While scholars often refer to a Christian New Testament consensus emerging within the timeframe of the fourth and fifth centuries (TCD, 4-5, 291), a larger amount of disagreement persisted regarding the Old Testament in Christian circles. Michael Holmes writes:
"The relative uniformity characteristic of the New Testament canon was never achieved for the Septuagintal canon." (OES, 414)
There is no Christian Old Testament canonical consensus that's comparable to the New Testament consensus. And if a Jewish Old Testament consensus contradicts a Christian tendency to include more books in the Old Testament, then a choice has to be made between the two. The Jewish Old Testament consensus includes pre-Christian Jews and Jews who were contemporary with Jesus, so it's not just a matter of what was believed by Jews who rejected Christianity. And the Jewish people didn't just not include the Apocryphal books, as if they were open to accepting them in the future. Rather, they dated the closing of the Old Testament canon prior to the time of the Apocrypha and said that the Apocryphal books are to be excluded.
The popularity of some Apocryphal books among Christians does carry some weight. It increases the credibility of the canonicity of those books. But other evidence, like what I've outlined above, has to be taken into account as well. The issue is more complicated than either agreeing with all of Athanasius' Biblical canon or disagreeing with all of it.