Do we know which books are inspired and belong in the Bible simply by reading them? Are all the biblical books self-attesting, so that no church is needed to determine the biblical canon? This is what many of our Protestant brethren argue.
There are indeed several internal biblical evidences of inspiration and canonicity, yet (despite this fact), there were many differences in the early Church regarding biblical books. Many now-accepted books were questioned, and many non-biblical books were thought to be canonical.
These internal evidences for inspiration vary greatly. For example, the author of Hebrews doesn't identify himself (nor does the author of 2 and 3 John), and denies being an apostle (Heb. 2:3).
The author of the book of James does not, in his epistle, make the claim to being an apostle (Jas. 1:1) -- though the likelihood is that he probably was. Jude was questioned because it cited the Book of Enoch (Jude 14-15) and possibly the Assumption of Moses (Jude 9). Only the author of Revelation claims direct inspiration.
But nothing illustrates the falsity of the claim of “self-attesting” books better than the history of the process of canonization itself. Church authority was needed to establish the canon once and for all. If everything were so obvious, how could there be so many differences?
The awareness of a canon itself didn't even become prominent until the end of the 2nd century. St. Athanasius was the first person to list our present 27 New Testament books, in the year 367: more than 300 years after the death of Jesus. Many other “anomalous” facts indicate the numerous substantial difficulties of canonicity.
It is historical fact that many biblical books were slowly accepted. St. Justin Martyr (d. c. 165) didn't recognize Philippians or 1 Timothy. The Muratorian Canon (c. 190) excluded Hebrews, James, 1 Peter, and 2 Peter. The Council of Nicaea in 325 questioned the canonicity of James, 2 Peter, 2 John, 3 John, and Jude.
Even up to the late 4th century, the book of James had not even been quoted in the west. The books of Hebrews, 2 Peter, 2 and 3 John, and Revelation were still being disputed at that late date. Revelation was rejected by St. Cyril of Jerusalem (d. 386), St. John Chrysostom (d. 407), and St. Gregory Nazianzen (d. 389).
None of this is consistent with the notion that it is easy to determine a biblical book (i.e., an inspired book) simply by reading it. Believers in the early Church (such as St. Athanasius or St. Augustine) were just as zealous for the Bible and Christian truth as Christians today. Yet they often disagreed on this score.
Moreover, we observe that many non-Scriptural books were regarded as Scripture by many important people and lists of canonical books in the early Church.
The Gospels of St. Justin Martyr contained apocryphal materials. The Epistle of Barnabas and the Didache were regarded as Scripture by St. Clement of Alexandria (d. c. 215) and Origen (d. c. 254); so was the Shepherd of Hermas, by St. Irenaeus (d. c. 200), Tertullian (d. c. 225), Origen, and St. Clement of Alexandria.
The Muratorian Canon of c. 190 included the Apocalypse of Peter and Wisdom of Solomon. The well-known Codex Sinaiticus of the late fourth century still included the Epistle of Barnabas and the Shepherd of Hermas.
Protestants counter-reply that the existence of historical disagreements on the canon doesn't prove that it was unable to be determined by a close study of the biblical books. All this shows is that Church fathers were fallible men, just like everyone else. The more the Bible was studied, the more men came to understand which books were truly inspired and which were not, by the clear indications in the books themselves.
It's very easy to make such (somewhat logically circular) claims, and “hindsight is 20-20”; however, there is no way to test or disprove (or, for that matter, prove) them other than by looking at what actually happened in history. Are we to believe that the same people in the early Church who developed doctrines like the Holy Trinity, didn't understand which books belonged in the Bible as well as we do today, because they were poor readers or slow to comprehend what is “obvious” to us?
The fact remains that there were disagreements because some books were not all that clearly inspired (and other non-biblical books seemed to be). Indeed, we expect men to disagree; all the more reason for an authority.
Thus, the Church decided on the issue of the canon in the councils of Hippo (393) and Carthage (397). It is sometimes objected that these were merely local councils. But they were preceded by a Roman Council (382) of identical opinion, and were ratified by Popes Innocent I (405, 414) and Gelasius I (495). The 6th Council of Carthage (419) also concurred.
The great Protestant Bible scholar F. F. Bruce stated:
When we think of Jesus and his Palestinian apostles, then, we may be confident that they agreed with contemporary leaders in Israel about the contents of the canon. We cannot say confidently that they accepted Esther, Ecclesiastes or the Song of Songs as scripture, . . .
While the New Testament writers all used the Septuagint, to a greater or lesser degree, none of them tells us precisely what the limits of its contents were . . . We cannot say with absolute certainty, for example, if Paul treated Esther or the Song of Songs as scripture any more than we can say if those books belonged to the Bible which Jesus knew and used.
. . . only one book of the New Testament explicitly claims prophetic inspiration . . . It is unlikely, for example, that the Spirit's witness would enable a reader to discern that Ecclesiastes is the word of God while Ecclesiasticus is not . . . (The Canon of Scripture, Downers Grove, Illinois: InterVarsity Press, 1988, 41, 50, 280-282)