You may sometimes hear the objection that there were lots of other gospels and books floating around at the time when the 27 books of the New Testament were standardized. The right way to answer this problem is to ask for a particular book that the challenger would like included and then to take a look at factors like the date it was written, who wrote it, and where it was written. When you look at these factors, it becomes obvious why the other books were left out.
Consider an article by Dr. Charles Quarles, who has written against an early dating of a “left out” book called the “Gospel of Peter”. Why was it left out? Because Christian are mean? Maybe there’s a historical reason why these books are not included.
An impressive number of clues suggest that this gospel [Peter] postdates even the latest New Testament book and belongs to the mid-second century. First, a close analysis of verbal parallels shared by the Gospel of Peter and the Gospel of Matthew suggests that the Gospel of Peter postdates Matthew and utilized that Gospel as a source… an examination of the vocabulary, grammar, and style of the two documents strongly favors the dependence of the Gospel of Peter on Matthew. Robert Gundry, one of the most respected experts on issues related to Matthew’s style, called the phrase a “series of Mattheanisms” (Gundry, Matthew [Grand Rapids: Eerdmans, 1994], 584). Similarly, John Meier noted “when it comes to who is dependent on whom, all the signs point to Matthews priority. . . . The clause is a tissue of Matthean vocabulary and style, a vocabulary and style almost totally absent from the rest of the Gospel of Peter” (Meier, Marginal Jews, 1:117). This is consistent with a number of other Matthean features appear in the Gospel of Peter that all point to the dependence of the Gospel of Peter on Matthew.
Second, other features of the Gospel of Peter suggest that the gospel not only postdates Matthew, but even postdates the latest book of the NT canon, the Book of Revelation. For example, although Matthew indicates that the Roman guard sealed the tomb of Jesus, Gospel of Peter 8:33 adds that it was sealed with seven seals. The reference to the seven seals conflicts with the immediate context. Gospel of Peter 8:32-33 states that all the witnesses present sealed the tomb. However, a minimum of nine witnesses were present leading readers to expect at least nine seals. The best explanation for the awkward reference to the seven seals is that the detail was drawn from Revelation 5:1. This allusion to Revelation fits well with the Gospel of Peter 9:35 and 12:50 reference to the day of Jesus’ resurrection as the “Lord’s Day” since this terminology only appears in Revelation in the NT and first in Revelation out of all ancient Christian literature. The reference to the “Lord’s Day” in the Gospel of Peter is a shortened form that appears to be a later development from the original form appearing in Revelation.
Still other features of the Gospel of Peter fit best with the historical data if the Gospel of Peter was produced in the mid-second century. The Gospel of Peter assumes the doctrine of Jesus’ descent into Hades to preach to the dead. However, this doctrine first appears in the words of Justin Martyr around AD 150. The talking cross is a feature of other second-century literature. The Epistula Apostolorum 16 states that during the second coming Jesus will be carried on the wings of the clouds with his cross going on before him. Similarly, the Ethiopic Apocalypse of Peter 1 describes the returning Christ as coming in a glory seven times as bright as the sun and with his cross going before his face. In a similar fashion, beginning in the late first century, Christian texts describe Christ as possessing gigantic stature. In an allegorical depiction of Jesus’ supremacy and authority over the church, Shepherd of Hermas 83:1 described Christ as of such lofty stature that he stood taller than a tower. 4 Ezra 2:43, a portion of 4 Ezra dating to the middle or late third century, referred to the unusual height of the Son of God. These shared compositional strategies and features make the most sense if these documents and the Gospel of Peter were composed in the same milieu.
It turns out that Quarles has actually debated the views he presents in this article against John Dominic Crossan, the main proponent of the view that the Gospel of Peter is early. You can buy the audio on CDs here, or you can get the book. The CDs are highly recommended, but the book leaves out all the dialog, so I don’t recommend it.
And you can read about two more rejected books, the Gospel of Thomas and the Gospel of Judas, as well. The authors of those two articles are Craig Blomberg and Craig A. Evans, respectively. Craig Evans is also involved in the debate I mentioned with Crossan. He was able to debunk another “lost book of the Bible” called “Secret Mark”, which turned out to be a hoax.