Understandably, the below line is a lot to think about, but it’s worth considering carefully. The statement tells us that we know the Bible is God’s Word because it is self-authenticating.
Some may object to the Word of God should be confirmed by some other source of authority such as history or science. But if a source of authority appeals to some other source of authority, than the source to which it appeals is ultimate authority.
Westminster Q 4. How doth it appear that the Scriptures are the Word of God?
A. The Scriptures manifest themselves to be the Word of God, by their majesty and purity, by the consent of all the parts, and the scope of the whole, which is to give all glory to God; by their light and power to convince and convert sinners, to comfort and build up believers unto salvation: but the Spirit of God bearing witness by and with the Scriptures in the heart of man, is alone able fully to persuade it that they are the very Word of God.