There are a number of discussions these days about the Biblical canon, about the way it was formed, about the different canons of various communities of faith, and so on. One of the more interesting questions is: What is the function of canon? That is, people wonder what exactly is a list of books supposed to accomplish. The simple answer is that canon is a function of catechesis.
Think about it. When we speak (or spoke, as the case may be) of the canon of great literature in school, the context of such a list of great works of literature was specifically didactic. A true familiarity with the great works of literature was not simply an expected hurdle of the academy, but was actually training in both the recognition and production of good writing, as well as the passing on of a cultural patrimony, the treasures of the past, to a new generation.
The Biblical canons work the same way. Their context lies in maintaining a list of books considered by teaching authorities as canonical, that is, adhering to the Rule of Faith. In the past in both Christian and Jewish communities, during the number of centuries before doctrines and practices were truly settled, the canons within both were also in flux. As the Rule of Faith changed and came to more perfect delineation in each, so also the canons were adjusted to reflect this. This would explain why at one point some books appeared to be Scripture, while later they were classed as apocryphal, or merely good reading if they were lucky.
The above idea is something that I’ll be looking into more deeply, but it came from realizing that a number of those works which list the books of the canon do so in the context of instruction in proper faith (catechesis is the strictest sense), and some explicitly mention that fact, for instance, Athanasius of Alexandria in his famous Thirty-Ninth Festal Letter. Unfortunately, the beginning of that letter is lost, as is the context for various of the lists preserved only by Eusebius in his systematizing survey in the Ecclesiastical History.
Anyhow, more on that some other time, in more detail.