John Calvin's Institutes: 1.6.1

Scripture Is Needed as Guide and Teacher for Anyone Who Would Come to God the Creator

1. God bestows the actual knowledge of himself upon us only in the Scriptures

That brightness which is bornein upon the eyes of all men both in heaven and on earth is more than enough to withdraw all support from men's ingratitude - just as God, to involve the human race in the same guilt, sets forth to all without exception his presence portrayed in his creatures. Despite this, it is needful that another and better help be added to direct us aright to the very Creator of the universe. It was not in vain, then, that he added the light of his Word by which to become known unto salvation; and he regarded as worthy of this privilege those whom he pleased to gather more closely and intimately to himself.

For because he saw the minds of all men tossed and agitated, after he chose the Jews as his very own flock, he fenced them about that they might not sink into oblivion as others had. With good reason he holds us by the same means in the pure knowledge of himself, since otherwise even those who seem to stand firm before all others would soon melt away. Just as old or bleary-eyed men and those with weak vision, if you thrust before them a most beautiful volume, even if they recognize it to be some sort of writing, yet can scarcely construe two words, but with the aid of spectacles will begin to read distinctly; so Scripture, gathering up the otherwise confused knowledge of God in our minds, having dispersed our dullness, clearly shows us the true God.

This, therefore, is a special gift, where God, to instruct the church, not merely uses mute teachers but also opens his own most hallowed lips. Not only does he teach the elect to look upon a god, but also shows himself as the God upon whom they are to look. He has from the beginning maintained this plan for his church, so that besides these common proofs he also put forth his Word, which is a more direct and more certain mark whereby he is to be recognized.

Excerpt from Calvin: Institutes fo the Christian Religion 1, ed. McNeill, John T. Westminster, 1960, pg. 69-70