John Calvin on Proof that Scripture is the Word of God

"For it is not to be accounted of no consequence, that, from the first publication of Scripture, so many ages have uniformly concurred in yielding obedience to it, and that, notwithstanding of the many extraordinary attempts which Satan and the whole world have made to oppress and overthrow it, or completely efface it from the memory of men, it has flourished like the palm tree and continued invincible. Though in old times there was scarcely a sophist or orator of any note who did not exert his powers against it, their efforts proved unavailing. The powers of the earth armed themselves for its destruction, but all their attempts vanished into smoke. When thus powerfully assailed on every side, how could it have resisted if it had trusted only to human aid? Nay, its divine origin is more completely established by the fact, that when all human wishes were against it, it advanced by its own energy. Add that it was not a single city or a single nation that concurred in receiving and embracing it. Its authority was recognised as far and as wide as the world extends - various nations who had nothing else in common entering for this purpose into a holy league. ....Again, with what confidence does it become us to subscribe to a doctrine attested and confirmed by the blood of so many saints? They, when once they had embraced it, hesitated not boldly and intrepidly, and even with great alacrity, to meet death in its defense. Being transmitted to us with such an earnest, who of us shall not receive it with firm and unshaken conviction? It is therefore no small proof of the authority of Scripture, that it was sealed with the blood of so many witnesses, especially when it is considered that in bearing testimony to the faith, they met death not with fanatical enthusiasm, (as erring spirits are sometimes wont to do,) but with a firm and constant, yet sober godly zeal. There are other reasons, neither few nor feeble, by which the dignity and majesty of the Scriptures may be not only proved to the pious, but also completely vindicated against the cavils of slanderers. These, however, cannot of themselves produce a firm faith in Scripture until our heavenly Father manifest his presence in it, and thereby secure implicit reverence for it. Then only, therefore, does Scripture suffice to give a saving knowledge of God when its certainty is founded on the inward persuasion of the Holy Spirit. Still the human testimonies which go to confirm it will not be without effect, if they are used in subordination to that chief and highest proof, as secondary helps to our weakness. But it is foolish to attempt to prove to infidels that the Scripture is the Word of God. This it cannot be known to be, except by faith. Justly, therefore, does Augustine remind us, that every man who would have any understanding in such high matters must previously possess piety and mental peace."

John Calvin - The Institutes of Christian Religion