Credibility of doctrine is not established until we are persuaded beyond doubt that God is its Author. Thus, the highest proof of Scripture derives in general from the fact that God in person speaks in it. The prophets and apostles do not boast either of their keenness or of anything that obtains credit for them as they speak; nor do they dwell upon rational proofs. Rather, they bring forward God’s holy name, that by it the whole world may be brought into obedience to him. Now we ought to see how apparent it is not only by plausible opinion but by clear truth that they do not call upon God’s name heedlessly or falsely. If we desire to provide in the best way for our consciences—that they may not be perpetually beset by the instability of doubt or vacillation, and that they may not also boggle at the smallest quibbles—we ought to seek our conviction in a higher place than human reasons, judgments, or conjectures, that is, in the secret testimony of the Spirit. True, if we wished to proceed by arguments, we might advance many things that would easily prove—if there is any god in heaven—that the law, the prophets, and the gospel come from him. Indeed, ever so learned men, endowed with the highest judgment, rise up in opposition and bring to bear and display all their mental powers in this debate. Yet, unless they become hardened to the point of hopeless impudence, this confession will be wrested from them: that they see manifest signs of God speaking in Scripture. From this it is clear that the teaching of Scripture is from heaven. And a little later we shall see that all the books of Sacred Scripture far surpass all other writings. Yes, if we turn pure eyes and upright senses toward it, the majesty of God will immediately come to view, subdue our bold rejection, and compel us to obey.
Institutes of the Christian Religion, Volumes 1 & 2, ed. John T. McNeill, trans. Ford Lewis Battles, The Library of Christian Classics (Louisville, KY: Westminster John Knox Press, 2011) Vol. 1.7.3. p. 78-79.