A full explanation of the process of deciding on the New Testament canon would require a book-length response, and indeed books have been written about it; however, it is possible to give a basic overview in a short article.
The canon is the list of authoritative books that make up the New Testament. There were many other early Christian documents, and some of them may have been very useful while others were heretical. The canon is the list of those that God has given to the church by the inspiration of the Holy Spirit. Skeptics often say that the early church was diverse and, as time passed, one version of Christianity won out over the other types. The “winners” decided which books would be authoritative, and, of course, they chose the books that they agreed with or that agreed with them. Furthermore, it is often claimed that the church simply decided which books to include in the New Testament centuries after Jesus and the apostles had left the scene. (This implies that Jesus, through the Holy Spirit, was not involved in the process at all!)
It is important to note that church leadership did not decide which books to include in the canon as much as they attempted to discover which books God had actually given to the church and should therefore be included. When attempting to determine which books were inspired and authoritative (books that should be included in the canon), the early church had three primary requirements:
• Apostolic Authority: Christ gave His apostles the task of preserving His teaching and taking it to all the world. For a book to be included in the canon, it had to be linked to an apostle or to someone who had seen the risen Jesus and had heard His teaching in person. Some of the books were written by apostles directly: Matthew, John, and Peter all wrote books included in the canon. The Gospel According to Mark is said to have been based on the preaching of Peter. Luke wrote Luke and Acts based on eyewitness interviews and firsthand documents (Luke 1:1–4). He was also a traveling companion of the apostle Paul and experienced many of the events in Acts firsthand. James and Jude were written by the half-brothers of Jesus and were not believers during Jesus’ lifetime. However, Jesus appeared to his brother James after the resurrection (1 Corinthians 15:7), and he became a believer. Such an appearance is not reported for Jude, but it can be safely assumed that he had heard Jesus’ teaching and that something spectacular made him change his mind about Jesus—most likely a post-resurrection appearance. Jesus appeared to Paul directly and commissioned him to be an apostle.
There were other books that may been helpful to Christians, but, if they did not have an apostolic connection, they were rejected as non-canonical. Some books were written in the name of an apostle, but, if it was evident he did not actually write it, that book was rejected.
• Orthodox Doctrine: There were many early documents that claimed to teach Christian doctrine but were in error. Much of the New Testament was written to combat these errors. Any document that contradicted the accepted teaching of the apostles was rejected. The apostles’ teaching was transmitted orally for years before the New Testament as we know it existed. Oral transmission within cultures that practice it has been shown to be very accurate—not like the “telephone game” to which it is often compared.
• Broad-Based Acceptance: There were a number of other books that may have been helpful and doctrinally correct and were used by portions of the church in various locations. However, to be considered canonical, a book had to have broad-based acceptance and recognition of its authoritative nature across the Christian world. Letters written by Paul to churches in Asia Minor were saved, copied, and circulated all over the civilized world, and Christians all over the world recognized their authoritative nature. This is what we would expect if God was actually involved in the process of deciding the canon.
As these tests of authenticity were applied, 27 books began to emerge. For a while there were some doubts or disputes about a book here or there, but the 27 books of the New Testament that are accepted by Christians today were the ones that emerged as a result of the application of the above guidelines. As this view of the canon emerged, various church councils and synods gave formal acknowledgment of what the church had organically come to recognize. (This is somewhat similar to how the term classic is applied to literary works. No one person decides that a certain book should be a “classic” of English literature. The “classic” status just emerges based on the intrinsic qualities of the book and its broad-based acceptance.)
The Synod of Laodicea (363) forbade the use of several non-canonical books. A formal list of canonical books was not given, but the difference between the two kinds of books was obviously evident, and none of the forbidden books were later accepted as canonical.
The Council of Hippo (393) stated that the 27 books in the New Testament were canonical.
The Synod of Carthage (397) stated that only canonical books should be read in the churches, and it listed the 27 books of the New Testament.
The Council of Carthage (419) reaffirmed the existing canon.
Prior to these councils, many early church leaders also listed books that were considered authoritative in their times. There was the occasional inclusion of a book that was ultimately excluded or some question about a book that was ultimately included, but, for the most part, there is remarkable agreement about which books were inspired and authoritative.
We accept by faith that the canon is correct; however, it is not blind faith. The early church had very specific ideas about what type of book should be included in the canon, and modern Christians can affirm their decisions. They were certainly in a better position than we to make this determination, so it would seem to be the height of hubris to charge them with error.