The Self-Attestation of the Scriptures

Here is Dr. Greg Bahnsen on the Scripture’s own testimony to itself:

Throughout its record the Bible presupposes its own authority.  For instance, the Old Testament is often cited in the New Testament with such formulas as “God says” or “the Holy Spirit says” (as in Acts 1:16; 3:24-25; 2 Cor. 6:16).  What Scripture says is identified with what God says (e.g., Gal. 3:8; Rom. 9:16).  For that reason all theological arguments are settled decisively by the inherent authority signified in the formula “it stands written” (literal translation).  The same authority attaches to the writings of the apostles (1 Cor. 15:1-2; 2 Thess. 2:15; 3:14), since these writings are placed on a par with the Old Testament Scriptures (2 Peter 3:15-16; Rev. 1:3).  Apostolic Scripture often has the common formula “it stands written” applied to it (e.g., John 20:31).  Therefore the Old and New Testaments are presented in the Bible itself as the authoritative, written, Word of God. [From his essay “The Inerrancy of the Autographa” in Inerrancy, ed. Norm Geisler]

We believe Scripture because God gave it, He is the author of it, He spoke it. Thus, the Scriptures are inherently authoritative by virtue of what they are, viz., God’s word.