Summa summae S. Thomae, Tomus III

[A mystery, or an arcane thing, is a truth far removed from our understanding: not indeed in the sense that it lies wholly hidden from us, for we truly know its terms, but because we do not attain the connection of its terms, whence it comes about that we scarcely comprehend it at all. Deists deny that mysteries can be revealed by God. Against whom:

I answer. Affirmatively.

Proof. For there are given truths that surpass the keenness of our mind. Therefore God can reveal them.

A mystery exists as regards us even in the natural order. That man is composed of soul and body united to one another is certain. But in what manner the composite resulting from this union is put together, and how the soul influences the body, and in turn the body the soul, these things altogether pass our understanding. Although bodies are more obvious to us, never has it been permitted to philosophers to determine their intimate nature. However far physicists have advanced in the knowledge of nature, they have not been able to assign the first causes of the laws and forces they have discovered. Whence, as far as one can see, this whole universe of things is a mystery. Moreover, every creature, though incomprehensible, is finite. Why then should truths of this kind not be found in God, whose nature is understood only as infinite? Therefore there are given truths that surpass the keenness of our mind.

Now, what could stand in the way of God's manifesting some of these truths to us, if it so please him, whether to exercise our faith, or to make trial of our obedience and compliance toward him? Surely no repugnancy is perceived on this side. Therefore God can reveal these truths to us.

You will object: God cannot reveal to man what man cannot admit. Now man cannot admit anything except what reason evidently demonstrates to be true, and such things are not mysteries. Therefore God cannot reveal them.

I answer. Let the major pass, or rather I even grant it. For it cannot be supposed that God would reveal to man something which man could not admit from any motive whatsoever. I distinguish the minor. That man cannot admit anything except what reason demonstrates to be true with evidence either intrinsic or extrinsic, I concede; intrinsic only, I deny. For if nothing ought to be admitted unless it is intrinsically evident, very many natural truths would be rejected; for if we tried to scrutinize them to the bottom, before long some mystery occurs that puts an end to our inquiry. It is no wonder, therefore, if truths pertaining to the supernatural order are not intrinsically evident, since they exceed the grasp of our reason. But if their terms are understood, and the historical fact of divine revelation is proved, they become evidently credible from an extrinsic motive, namely on account of the authority of God manifesting them. And this suffices to make the assent of the mind not only reasonable and legitimate, but altogether obligatory. Concerning the possibility and fittingness of supernatural revelation the Vatican Council thus decrees, de Revelatione, canons 2 and 3: « If anyone shall say that it cannot come to pass, or that it is not expedient, that man be taught about God and the worship to be rendered to him through divine revelation: let him be anathema. » — « If anyone shall say that man cannot be divinely raised up to a knowledge and perfection exceeding his nature, but that from himself he can and finally ought, by unceasing progress, to attain the possession of all truth and all goodness: let him be anathema. »]