(CG 3/55). That the Created Intelligence does not comprehend the Divine Subs... (Book 3. God, the End of Creatures) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

THEN only does the knowledge of a principle necessitate the knowledge of all its effects, when the principle is thoroughly comprehended by the understanding: for so a principle is known to the whole extent of its power, all its effects being known as caused by it. But through the divine essence other things are known as effects from their cause. Since then created intelligence cannot know the divine substance so as to comprehend it, there is no necessity for it in seeing the divine substance to see all things that can be known thereby.

3. The extent of any power is measured by the objects to which it reaches. To know then all the objects to which any power reaches is to comprehend the power itself. But the divine power, being infinite, can be comprehended by no created intelligence, as neither can the divine essence (Chap. LV). Neither then can any created intelligence know all the objects to which the divine power extends.

5. No cognitive faculty knows anything except under the aspect of its proper object: thus by sight we know things only as coloured. Now the proper object of intelligence is whatever is in the substance of a thing. Therefore whatever the intelligence knows of a thing, it knows by a knowledge of the substance of the thing. If ever we know the substance of a thing by its accidents, that happens accidentally, inasmuch as our intellectual knowledge arises from sense, and thus we need to arrive at an intellectual view of substance through a knowledge of accidents: wherefore this does not take place in mathematics, but in the natural sciences only. Whatever therefore in a thing cannot be known by a knowledge of its substance, must remain unknown to the knowing mind. But what a voluntary agent wishes cannot be known by a knowledge of his substance: for the will does not tend to its objects altogether by natural necessity: hence 'will' and 'nature' are counted two distinct active principles. What therefore a voluntary agent wills is not knowable except haply through certain effects, as, when we see one acting voluntarily, we know what he has willed: or it may be known in its cause, as God knows our wills, as He knows other effects of His production, by the fact of His being to us the cause of willing (B. I, Chap. LXVIII ad fin.): or it may be known by one intimating his will to another, as when one expresses his desire by speech. Since then many things depend on the absolute will of God, as has been partly shown already, and will hereafter appear, a created intelligence, even though seeing the substance of God, does not for all that see all that God sees by his substance.

It may be objected that God's substance is something greater than all that He can make, or understand, or will beyond Himself; and that therefore, if a created intelligence can see the substance of God, much more can it know all that God through Himself either understands or wills or can do. But on careful study we see that it is not one and the same thing for an object to be known in itself and known in its cause. There are things easy enough to know in themselves, but not easily known in their causes. Though it is true that it is a grander thing to have understanding of the divine substance than to understand anything else, knowable in itself, away from that substance, still it is more perfect knowledge to know the divine substance, and in it to see its effects, than to know the divine substance without seeing its effects. Now the seeing of the divine substance may be without comprehension of it: but to have all things rendered intelligible through that substance and actually known, that cannot come about without comprehension.