I’ve heard people say, “I’d love to believe the Bible is true, but it’s so messed up now. They’ve mistranslated it, and left out this or that gospel. It just isn’t reliable. We can’t know what God really meant anymore.”
A logical response includes some giant propositions, but ones with which believers will agree. First, God is all-powerful. He is able to create a message and preserve it through time. Second, God doesn’t want anyone to perish (2 Peter 3:9). Jesus gave His life to save us, and the instructions for how this works figure hugely in God’s message. It follows that God wants this message preserved. Finally, if God is able to convey a message, and He wants to convey that message, it makes sense that He has guarded it to this day.
What books are the message of God? And what writings are fraudulent, heretical, or just regular old uninspired writing? This is where the Canon comes in.

Canon?

Many people have crippling misconceptions about the Biblical Canon; what books are included, why these and not others, and how the list was formalized. A faulty understanding of this part of Christianity’s history can knock the feet from under your faith before it has a chance to grow properly. So let’s take a look at how we arrived at the sixty-six book Canon.
The word canon is from reed (in Greek: kanon, in English: cane). “The reed was used as a measuring rod, and came to mean “standard””.(1) The meaning of the word continued to evolve until it meant “an officially accepted list of books.” In this definition is a key point: church leaders didn’t choose the list of books.(2) They merely examined the books that Christians were already using and accepting as Scripture, recognized them formally, and wrote them down for future reference. By “accepting as Scripture,” I mean that Christians took certain books and letters to be inspired by God—written by humans being guided by God to say what He wanted said.
Discussions about the Canon started as early as A.D. 90, at Jamnia (when rabbis confirmed the Jewish Canon—Old Testament books). They continued until “a church council in Carthage in A.D. 397 when the New Testament canon was fixed.”(3)

The Old Testament Canon

Protestants and Catholic Bibles differ slightly in which books comprise the Old Testament. Protestants accept as canonical the same OT content as the Jews, though in our Bible we divide the books differently, and change the order in which they appear. The Catholic Bible makes additions to several OT books, and includes several apocryphal books not recognized as Scripture by the Jews.

The New Testament Canon

Many New Testament books started out as letters circulated among the churches. Believers needed to know which letters were actually written by the apostles or their close associates. The authority of many books was confirmed by other apostles or eyewitnesses (see 2 Peter 3:1-16 and Jude 17 and 18). But by A.D. 140, heretical and fraudulent books were also making the rounds. Some were obvious fakes, but others were more subtle, sounding authentic but not telling the truth about God. If a book did not agree with the entire body of Scripture, it was not inspired, and would lead the church into error. These were gradually weeded out. Remember, God was orchestrating the preservation of His message, and He used the Body of Christ to do it. Only books widely recognized by the church as authentic and inspired were included in the collection eventually described as the Canon.

(1) Josh McDowell, The New Evidence That Demands a Verdict (Nashville: Thomas Nelson, 1999) 21.
(2) McDowell 21.
(3) Paul E. Little, Know Why You Believe (Illinois: InterVarsity Press, 2000) 82.