The canon, the list of books that are regarded as inspired and authoritative, places a “hedge” around God’s special written revelation to separate it from other Jewish and Christian writings. The canons of the Old Testament and New Testament are separate developments. The coming into existence of the Old Testament canon is lost in the mists of time. In contrast, the finalization of the New Testament canon is well documented and was a complex process. It took until AD 367 for it to be finalized.
Anytime a previously unknown early Christian or Jewish writing is discovered there are people who think the document will reshape our understanding of Christianity. This has, fortunately, not turned out to have happened. Our canons are sufficient. it is us that is to be shaped by them.
The Old Testament canon accepted by Protestants consists of thirty-nine books that originated over a period of about 1,000 years. Jews and Roman Catholics accept fifteen additional books known as the Apocrypha as a secondary addition to the Old Testament and include them in their Bibles as lesser writings.
The Old Testament was adopted by Christians as essential to our beliefs because of its intimate connection with Jesus and the New Testament. Jesus and the writers of the New Testament extensively quote passages from the Old Testament and Jesus’ life was framed in the context of Old Testament prophecies.
The closing of the New Testament canon means that for over 1,600 years Christians have been hearing and then both hearing and reading the same New Testament. Or perhaps I should say almost the same New Testament. Variants in the copies and the need of most of us for translations mean we do not all have exactly the same book. However, when we read the Fathers, for instance, we can see that they have read and are quoting essentially the same New Testament we have. I believe this is one way God shows us our unity with the Christians who have come before us.