How can we know which books belong in the Bible? What about the apocryphal books and “Gospels” that were not included in the canon? How can we know our Bibles are complete?
I’m happy to offer some information, but a thorough answer would require much more space than is available here. For this reason, I’m giving you a brief overview of the biblical canon and then, toward the end of the discussion, will suggest some books for further investigation.
It is clear that Jesus and the disciples recognized a particular set of books as God-breathed Scripture (see 2 Timothy 3:16). Paul calls these inspired writings the “oracles of God” and says they had been committed to the Jews (Romans 3:1–2). There is no evidence within the New Testament of disputes among the disciples of Jesus regarding which books made up the Scriptures they frequently referred to. On the contrary, the multitude of New Testament quotations from the Law, the Prophets, and the Writings leave the clear impression that there was universal agreement on which books were regarded as inspired of God.
In the Gospels, Jesus makes numerous references to these God-inspired books as “the Scriptures.” He states that every part of inspired Scripture refers to Him. This is what He is affirming in His reference to the threefold division of the Hebrew Scriptures—“the Law of Moses and the Prophets and the Psalms” (see Luke 24:44–45; cf. v. 27). Then, as we read through the New Testament, we see that there are a multitude of quotations from the Old Testament, affirming the writers held the same view of Scripture as Jesus; yet, there is no explicit reference to any of the books of the Apocrypha.
The Jews who met in the Council of Jamnia (held in either the late first or early second century CE) reviewed the tradition they had received from their forefathers and made no changes. They affirmed the same books their fathers before them affirmed, and those books were the same ones that make up our “Protestant” Old Testaments. Though some of the texts of the Apocrypha were included with the earliest Greek (Lxx, or Septuagint) manuscripts, the Jews of the Council of Jamnia did not accept them as Scripture, and their affirmation regarding accepted books reflects the tradition of their forefathers and, as we see from the scriptural references above, is consistent with the witness of the New Testament itself. I am not suggesting that the Jews of that council had any special authority; I’m simply saying that their conclusions were a witness to what had been widely understood and accepted at that time and in previous times.
Many Christian apologists and theologians from the early centuries until the Reformation rejected the apocryphal books. It’s not as if the Reformers just up and decided to cut out a section of Scripture that had always been accepted without dispute. They excluded the apocryphal texts because the historical witness demanded it! Those texts are important in that they give us some insight into a certain period of history, but they were simply never a part of the Sacred Scriptures.
The canon of Scripture was not formally defined until the Council of Trent (fourth session, April 4, 1546). It happened then because the Reformers had challenged it, stating that the apocryphal books were not authoritative Scripture.
Now, on to the New Testament. A common belief today is that the New Testament canon came about as a result of one group having its way through aggressively going after and stamping out competing groups, all of which operated under the broad umbrella of “Christianity.” The “victims,” of course, were probably kinder, more loving, and more tolerant and accepting of other groups. The more aggressive and less tolerant winners went on to form the Christianity that has come down to us. They tossed out (and burned) the books that didn’t fit their narrow, carnal-minded, patriarchal philosophy.
Of course, that’s a lot of nonsense! Manuscripts and fragments from the early patristic period show, by the multitude of quotations from existing New Testament writings, that the Gospels and many other of the books we find in our New Testament were accepted as apostolic—and therefore considered inspired of the Holy Spirit—very early; and when we examine Gnostic texts today, it is clear that these came later and obviously draw heavily from authentic Christian documents and stories that preceded them. The Gnostic philosophy comes across very clearly, and it quickly becomes clear to the unbiased reader that so-called Gnostic Christians were in a very different religious and philosophical category than the wider Christian community.
The Christian community of the post-apostolic period had no central authority that had the responsibility of preserving all inspired New Testament Scriptures. Instead, the many churches that made up the Christian community were themselves a witness to the apostolicity of the letters that circulated among them. By the fourth century, CE, there were lists of New Testament documents, and those lists were consistent with the Bible that has come down to us.
Contrary to contemporary “wisdom,” apostolic writings were already considered Scripture long before the last apostle died! Peter, on the Day of Pentecost, knew for certain that God, by way of the Holy Spirit, was speaking through him (Acts 2), and that his words were inspired of God and therefore infallibly true. Many of the “Comforter” promises of John 14–17 were specifically for the apostles and the foundational mission they were to accomplish. They understood that God was to speak through them just as He had spoken through the prophets in the Old Testament. That, no doubt, is one reason Peter could confidently include Paul’s epistles with “the rest of the Scriptures” (2 Peter 3:15– 16). So the modern notion that the apostles did not know they were writing Scripture and didn’t know the Spirit rested upon them and spoke through them as it had done with the prophets in Old Testament times is sheer nonsense. This is important because it shows that recognition of the inspiration and apostolicity of those letters is not an idea that came about at a time far removed from the apostles. Even if formal canonization did not occur until much later, that has nothing to do with the fact that the value of those documents was recognized the apostolic period itself.
So, through all of this, we should be able to see that history has left us an adequate witness to the authenticity of the Bible that has come down to us. And it makes sense—it’s a logical deduction—that if God saw to it that His “oracles” would be preserved through the Jews, He would also see to it that documents testifying of the Messiah and His assembly would be preserved for His people throughout the ages.
Your questions deserve more than the brief reply I offer here, so I refer you to some books that deal exhaustively with the issues surrounding the canon of Scripture and how we can know which books belong in the Bible. All of them can be purchased through Amazon.com: The Canon of Scripture by F.F. Bruce; The Old Testament Canon of the New Testament Church by Roger Beckwith; and Canon Revisited: Establishing the Origins and Authority of the New Testament Books by Michael J. Kruger.
I do not endorse all the views of the authors of these books, but I do think that on the critical issues regarding the scriptural canon you will find much helpful information within them. There are other helpful sources, but these three (or either of the three) will supply you with an abundance of evidence that the books that make up the “Protestant” Bible are the ones God inspired and preserved for the benefit of His people.