The authority of Scripture — the ground upon which the Bible ought to be believed and obeyed — rests wholly upon God, who is truth itself, and not upon the testimony of any man or church. The Westminster Confession teaches that Scripture is autopiston (self-authenticating): it carries its own evidence of divine origin. ^[raw/en/wcf-ch01-s04.md]
The Confession declares: "The authority of the Holy Scripture, for which it ought to be believed, and obeyed, dependeth not upon the testimony of any man, or church; but wholly upon God (who is truth itself) the author thereof: and therefore it is to be received, because it is the Word of God." ^[raw/en/wcf-ch01-s04.md]
This statement is the hinge upon which the entire Protestant doctrine of Scripture turns. Against Rome (which taught that Scripture's authority depends on the church's determination), and against rationalists (who subject Scripture to human reason), the Confession insists that the Bible carries the authority of God Himself.
1 Thessalonians 2:13 is pivotal: the Thessalonians received Paul's preaching "not as the word of men, but as it is in truth, the word of God." The authority was intrinsic, not conferred by the church.
Section 5 deepens this by affirming that "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." ^[raw/en/wcf-ch01-s05.md]
John Calvin argues that Scripture "bears upon the face of it as clear evidence of its truth, as white and black do of their colour, sweet and bitter of their taste." The evidence is not external but internal — the same Spirit who inspired the Word also illumines the reader.
Thomas Watson illustrates this memorably: "The king's proclamation is fixed on the pillar. The pillar holds it out, that all may read — but the proclamation does not receive its authority from the pillar, but from the king. So the church holds forth the Scriptures — but they do not receive their authority from the church, but from God."
Yet the Confession adds a crucial "nevertheless": "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." ^[raw/en/wcf-ch01-s05.md]
This is the great Reformed doctrine of the testimonium internum Spiritus Sancti — the internal testimony of the Holy Spirit. The external evidences can produce a "high and reverent esteem" for Scripture, but only the Spirit's inward witness produces saving faith. As Robert Shaw explains, there is a difference between historical faith (assent based on evidence) and saving faith (full persuasion wrought by the Spirit).
This internal witness does not bypass the Word; it works "by and with" it. The Spirit and the Word are knit together in an indissoluble union — a point equally vital for the doctrines of sufficiency-of-scripture and clarity-of-scripture.
The authority of Scripture grounds sola-scriptura: because Scripture carries God's own authority, it is the supreme judge of all controversies, the final court from which there is no appeal. This is what gave the martyrs their boldness — a conscience captive to the Word of God is free from every human tyranny.