Reply Obj. 1: It matters not to prophecy by what comparisons the thing prophesied is expressed; and so the Divine operation makes no change in a prophet in this respect. Yet if there be anything in him incompatible with prophecy, it is removed by the Divine power.
Reply Obj. 2: The considerations of science proceed from a natural cause, and nature cannot work without a previous disposition in matter. This cannot be said of God Who is the cause of prophecy.
Reply Obj. 3: A natural indisposition, if not removed, might be an obstacle to prophetic revelation, for instance if a man were altogether deprived of the natural senses. In the same way a man might be hindered from the act of prophesying by some very strong passion, whether of anger, or of concupiscence as in coition, or by any other passion. But such a natural indisposition as this is removed by the Divine power, which is the cause of prophecy. _______________________
FOURTH ARTICLE [II-II, Q. 172, Art. 4]
Whether a Good Life Is Requisite for Prophecy?
Objection 1: It would seem that a good life is requisite for prophecy. For it is written (Wis. 7:27) that the wisdom of God "through nations conveyeth herself into holy souls," and "maketh the friends of God, and prophets." Now there can be no holiness without a good life and sanctifying grace. Therefore prophecy cannot be without a good life and sanctifying grace.
Obj. 2: Further, secrets are not revealed save to a friend, according to John 15:15, "But I have called you friends, because all things whatsoever I have heard of My Father, I have made known to you." Now God reveals His secrets to the prophets (Amos 3:7). Therefore it would seem that the prophets are the friends of God; which is impossible without charity. Therefore seemingly prophecy cannot be without charity; and charity is impossible without sanctifying grace.
Obj. 3: Further, it is written (Matt. 7:15): "Beware of false prophets, who come to you in the clothing of sheep, but inwardly they are ravening wolves." Now all who are without grace are likened inwardly to a ravening wolf, and consequently all such are false prophets. Therefore no man is a true prophet except he be good by grace.
Obj. 4: Further, the Philosopher says (De Somn. et Vigil. [*Cf. De Divinat. per Somn. i, which is annexed to the work quoted]) that "if interpretation of dreams is from God, it is unfitting for it to be bestowed on any but the best." Now it is evident that the gift of prophecy is from God. Therefore the gift of prophecy is vouchsafed only to the best men.
On the contrary, To those who had said, "Lord, have we not prophesied in Thy name?" this reply is made: "I never knew you" (Matt. 7:22, 23). Now "the Lord knoweth who are His" (2 Tim. 2:19). Therefore prophecy can be in those who are not God's by grace.