This is the post #7 of the Calvin's Institutes summary series.
It is not church that gives Scripture its authority, rather, it is God, for He is the Author of it. In fact, it is the church that is founded upon Scripture. The church does recognise the divine qualities of Scripture because the saved ones are the ones whose minds are illumined by the Holy Spirit. More than reasons or other facts, the Holy Spirit Himself gives proof and assurance to those who believe that Scripture is the true Word of God. Trying to prove Scripture as the true Word of God by reason or other facts is a vain effort because that would be an attempt to build one's foundation of faith by men's effort rather than relying on God Himself. Nevertheless, the best reasons do agree with the true doctrine of Scripture.
Conclusion: "that those whom the Holy Spirit has inwardly taught truly rest upon Scripture, and that Scripture indeed is self-authenticated; hence it is not right to subject it to proof and reasoning. [...] Such, then, is a conviction that requires no reasons; such a knowledge with which the best reason agrees–in which the mind truly reposes more securely and constantly than in any reasons; such, finally, a feeling that can be born only of heavenly revelation. I speak of nothing other than what each believer experiences within himself–though my words fall far beneath a just explanation of the matter."