WLC Q.4: How doth it appear that the scriptures are of the word of God?
The scriptures manifest themselves to be the word of God, by their majesty (Hos. 8:12, 1 Cor. 2:6–7,13, Ps. 119:18,129) and purity; (Ps. 12:6, Ps. 119:140) by the consent of all the parts, (Acts 10:43, Acts 26:22) and the scope of the whole, which is to give all glory to God; (Rom. 3:19,27) by their light and power to convince and convert sinners, to comfort and build up believers unto salvation: (Acts 18:28, Heb. 4:12, James 1:18, Ps. 19:7–9, Rom. 15:4, Acts 20:32) 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. (John 16:13–14, 1 John 2:20,27, John 20:31)
WCF 1.5.
We may be moved and induced by the testimony of the Church to an high and reverend esteem of the Holy Scripture. (1 Tim. 3:15) And the heavenliness of the matter, the efficacy of the doctrine, the majesty of the style, the consent of all the parts, the scope of the whole (which is, to give all glory to God), the full discovery it makes of the only way of man’s salvation, the many other incomparable excellencies, and the entire perfection thereof, are arguments whereby it doth abundantly evidence itself to be the Word of God: yet notwithstanding, our full persuasion and assurance of the infallible truth and divine authority thereof, is from the inward work of the Holy Spirit bearing witness by and with the Word in our hearts. (1 John. 2:20, John 16:13–14, 1 Cor. 2:10–12, Isa. 59:21)