The completed Bible is called the canon, and periodically people question which books should be included in the canon. The explanation of this can be lengthy and multi-faceted, and include such topics as inspiration, dating, prophecy, and the role of the church leaders. Thus a full explanation of the topic cannot be exhausted in a blog such as this. For a more complete discussion, see the following:
A General Introduction to the Bible, by Geisler and Nix
The New Bible Dictionary, by Wood, Marshall, and Howard
Defending Your Faith, by Dan Story
Several Systematic Theology texts deal with this subject. Two of them with lengthy discussions are by Lewis Chafer and by Norman Geisler.
Of these, The New Bible Dictionary is arguably the most readable, and A General Introduction to the Bible the most comprehensive.
We must first note that canonicity is determined by God, not by men — humans then discover the canon. The books are not canonical because men voted on them, and canonicity is not determined by human decision. Rather, God determines canonicity, and man discovers canonicity. This is an important point, for the Bible is a divine book written by God to man.
In a brief summary, we can say that to be included in the Bible, Christian church fathers generally made decisions around the following:
- Is the book authoritative? Does the writing claim to be God’s word, from God’s spokesman?
- Was the book written by a prophet of God? Was the author proven correct in his sayings, practically and theologically?
- Is the book authenitic? Was it truly written by the prophet or apostle, or sanctioned by them?
- Was the writer confirmed by acts of God? Did the writer prove his prophetic authority by performing signs of a prophet?
- Did the message tell the truth about God? Does the message line up with what we know about God from observing the world (Romans 1:20) and by what we know from previous revelation?
- Does the book come with the power of God? Does it change lives, as a living and active book should (Heb. 4:12)?
- Was it accepted by the people of God?
These principles are not employed in a manner like one would solve a math formula, or investigate a chemical reaction, or study a mechanical operation. Rather, the principles were employed by wise men of God, some of whom claimed to know they were writing scriptures. For example, several passages in the New Testament refer to other writers of the New Testament as writing scripture (see 2 Pet. 3:16; 1 Tim. 5:18/Matt. 10:10; 1 Cor. 2:10, 13, 14:37; Gal.12; Rev. 1:1; Rev. 22:9; Rom. 16:26; 1 Thess. 2:13; Romans 2:16).
Much of the discussion about the books of the Bible centered around the questions listed above. Once these were answered, the vast majority of books became evident, and the inspired books became clear to the church fathers. Some books, such as Hebrews, do not have an author stated in the text, but once the church fathers agreed it came from the pen of an apostle, it was universally accepted.
To this I would add but one brief personal comment. To anyone familiar with the tone and message of such books as those accepted by everyone into the New Testament, picking up a book like The Gospel of Thomas becomes evidently clear that it is not inspired. The nature of the books is vastly different.
This brief attempt at explaining the nature of canonicity is admittedly inadequate. The format of a blog is insufficient to do the subject justice, and I make no claims that this has answered all questions. For more research, see the books referenced above.