One of the hardest questions for a Protestant or an Evangelical to answer is: who determines which books belong in the canon of Scripture? The common Protestant answer is that the canon is self-authenticating. The argument goes: over time, God’s people recognized which books were inspired and canonical since the books themselves testify to their own inspiration.
Is such an answer sufficient for determining the canon of Scripture? Unfortunately, such an answer does not sufficiently determine the canon since it raises the following questions: How does one know who is part of “God’s people”? Does one include Catholics in this group? What about the Eastern Orthodox and Oriental Orthodox? Does one include Gnostics, Montanists, Manicheans, Arians, Donatists, Novatians, Monophysites, Monothelites, Waldenses, Mormons, Jehovah’s Witnesses, etc. in this group? Depending on which groups are included as “God’s people” will determine which books will be included in the canon. Also, one must ask how does one know over time God’s people will recognize the canon? By what standard does one determine the answer to this question?
Such are the questions that must be answered by Protestants in order to claim the canon is self-authenticating. Apart from sufficient answers to such questions, Protestants cannot maintain the doctrine of Sola Scriptura, the view that the Scriptures alone are the final authority for each individual Christian. If Protestants cannot adequately defend this doctrine, the doctrine of Sola Scriptura, by providing cogent answers to the questions above, then they must abandon their schism and come back to the Catholic Church.