The term “canon” is borrowed from Greek, in which kanon means a rule—a standard for measurement. With respect to the Bible, it speaks of those books that met the standard and therefore were worthy of inclusion.
Since the fourth century kanon has been used by Christians to denote an authoritative list of the books belonging to the Old Testament or New Testament. There has long been some difference of opinion about which books should be included in the Old Testament. Indeed, even in pre-Christian times, the Samaritans rejected all its books except the Pentateuch; while, from about the second century b.c. onwards, pseudonymous works, usually of an apocalyptic character, claimed for themselves the status of inspired writings and found credence in certain circles.
In the rabbinical literature it is related that in the first few centuries of the Christian era certain sages disputed, on internal evidence, the canonicity of five Old Testament books (Ezekiel, Proverbs, Song of Songs, Ecclesiastes, Esther).
In the patristic period there was uncertainty among Christians whether the Apocrypha of the Greek and Latin Bibles were to be regarded as inspired or not. Difference on the last point came to a head at the Reformation, when the church of Rome insisted that the Apocrypha were part of the Old Testament, on an equal footing with the rest, while the Protestant churches denied this. Though some of the Protestant churches regarded the Apocrypha as edifying reading (the Church of England, for example, continued to include them in its lectionary “for example of life but not to establish any doctrine”), they were all agreed that, properly speaking, the Old Testament canon consists of the books of the Hebrew Bible—the books acknowledged by the Jews and endorsed in the teaching of the New Testament.
The Eastern Orthodox Church was for a time divided on this issue, but has recently tended more and more to come down on the Protestant side. What qualifies a book for a place in the canon of the Old Testament or New Testament is not just that it is ancient, informative and helpful, and has long been read and valued by God’s people, but that it has God’s authority for what it says. God spoke through its human author to teach his people what to believe and how to behave. It is not just a record of revelation, but the permanent written form of revelation. This is what we mean when we say that the Bible is “inspired,” and it makes the books of the Bible in this respect different from all other books.
This is an excerpt from The Origin of the Bible by F. F. Bruce, J. I. Packer, Philip Comfort, and Carl F. H. Henry. To read more, you can purchase this book from many Christian bookstores and online retailers, including Tyndale.com: https://www.tyndale.com/p/the-origin-of-the-bible/9781414379326
Beckwith, R. T., et al. The Origin of the Bible. Carol Stream, IL: Tyndale House Publishers, 2020.