Summa contra Gentiles3.152 Chapter CLII. That grace causes faith in us

Forasmuch as grace causes charity in us, it follows that faith also is caused in us by grace.

Because the movement whereby we are directed by grace to our last end, is voluntary and not compulsory, as we have shown. Now there cannot be voluntary movement towards the unknown. Consequently, for us to be directed voluntarily to our last end, grace must first of all provide us with knowledge of that end. But this knowledge cannot be one of clear vision, in this state of life, as we have already proved. Therefore it must be knowledge by faith.

Moreover. The mode of cognition in every cognitive being follows the mode of that being’s nature: hence the mode of cognition differs in the angel, man and dumb animals, according to the diversity of their several natures, as we have shown. Now, that man may attain to his last end, he receives a perfection in addition to and surpassing his nature, namely grace, as we have proved. Consequently, it behoves man to receive over and above his natural knowledge, a knowledge surpassing his natural reason. This is the knowledge of faith, which is of things unseen by natural reason.

Again. Whenever a thing is moved by an agent to that which is proper to that agent, the thing moved must needs at the outset be imperfectly subject to the impressions of the agent, such impressions being as it were foreign and improper thereto, until they become proper to it in the term of the movement: thus wood is at first heated by fire, and such heat is not proper to the wood, but something outside its nature; but in the end, when the wood is incandescent, the heat becomes proper and connatural to it. In like manner, when one is taught by a master, at first he must needs receive the master’s ideas, not as understanding them by himself, but as taking them in faith, through their being above his capacity, so to speak: but in the end, when he has been thoroughly taught, he will be able to understand them. Now, as we have shown already, we are directed to our last end by the assistance of divine grace. And our last end is the clear vision of the First Truth in itself, as we have proved. Therefore, before obtaining this end, man’s mind, with the assistance of divine grace, must needs be subject to God by believing.

Further. At the beginning of this work we set down the advantages for which it is necessary that man should receive the divine truth by believing therein. Whence we may conclude that it was necessary for faith to be produced in us by divine grace.

Hence the Apostle says (Ephes. ii. 8): By grace you are saved through faith: and that not of yourselves, for it is the gift of God.

Hereby we refute the error of the Pelagians who said that the beginning of faith in us is not from God, but from ourselves.