Summa Theologiae Moralis, vol. I: De Principiis

S. Th. II-II, q. 6 and 7 ; De Verit., q. 8 and q. 18, a. 3.

726. God is the cause of faith : a) because He externally proposes both the things to be believed which we cannot know without divine revelation, and the manifest signs by which we know that this revelation is divine. But b) this is not enough, for many knowing these things do not believe ; hence an interior cause is also required which moves man interiorly to assent to those things which are of faith : but not only the free will alone, which is insufficient for a supernatural act ; therefore God also interiorly through grace (habitual or actual alone) moves us to assent to revealed truths. « Since man, by assenting to those things which are of faith, is elevated above his nature, this must be in him from a higher principle moving him interiorly, which is God. And therefore faith, as to the assent which is the principal act of faith, is from God moving interiorly through grace » (q. 6, a. 1). Faith, therefore, since it is by grace, is of itself infused.

727. Faith is supernatural, not only objectively because it has as its object the very truth of God revealing supernatural things ; but also subjectively because it is produced by a supernatural principle, the grace of God, not only medicinal or healing but also elevating. For it is impossible that by the powers of nature we attain any object which is in itself supernatural as such¹] ; since faith, namely, is the beginning of salvation and the root of justification, it is the means by which we tend to an end in itself supernatural, but the means must be proportioned to the end. So the Council of Orange II defined, can. 5, 6, 7 ; and Trent, sess. 6, c. 6, can. 3 ; and Vat., sess. 3, c. 3, can. 5 against Hermes. — Cf. John VI, 44, 45, 64 ; Eph. II, 5, 8 ; 1 Cor. III, 7 ; 2 Cor. III, 5 ; Phil. I, 29.

Moreover, not only the act of faith itself, but also the very affection of credulity or motion of the will, as being the beginning of faith, is elicited by the powers of grace, as the Council of Orange II defined, can. 5 and 7, against the Semipelagians. For to tend toward a supernatural object, namely toward the act of faith, requires the powers of grace.

The judgment of credibility itself can perhaps be made by the powers of nature, because it has as its object the reasonableness of faith ; but when that judgment is immediately and ultimately practical (here and now it is to be believed by me, here and now you believe), so that it is made in order to supernatural faith and is the cause that we wish to believe and do believe, or that the will of believing follows it, then it deals with the supernatural object as such, namely the act of faith to be exercised, and pertains to the beginning of faith, and therefore cannot be made except by the powers of grace, as is certainly gathered from the same Council (can. 5) and from the Council of Milevis (can. 4). Cf. S. Augustine, l. 2, c. 2, ep. Pel., c. 8.

The act of faith and the judgment of credibility are elicited by the habit of theological faith in him who possesses it²] ; otherwise it is done only by the powers of actual grace. The pious affection of credulity itself, according to S. Thomas, is elicited by charity in the just man ; but in the sinner it is done only by the help of actual grace.

728. Observations. — 1° The powers of grace which are granted to our intellect, whether under the form of a habit or under the form of actual grace, so that it can believe, are called by the holy Fathers and theologians the light of faith : for just as by the light of reason we can know natural things, so by these powers, which elevate our intellect, we can supernaturally know supernatural things.

2° Faith elevates us to the supernatural and divine order ; hence the act of faith is supernatural not only in mode but in itself and as to substance : for it is divine, because as material and formal object it has God in Himself, such as can naturally be known only by Himself. Hence we believe the same truths which we shall see in heaven as mysteries, and indeed for the same motive : the first truth revealing them. The only difference is on the part of the condition of the object, which in heaven is clear, here remains obscure. Hence, as the beatific vision is an act of divine life, so also is faith.

3° The habit of faith not only causes the act of faith itself, but, as in other habits, its causality extends itself to other principal subordinate acts (I-II, q. 54, a. 4), whether they are preparatory acts of the principal act, or conservative of it. Hence, by the habit of faith are also produced both the acts pertaining to the previous judgment of credibility as was said in the preceding n°³]., and the acts by which (on account of the authority of the Church) are admitted truths not indeed in themselves revealed but connected with these, which are defined by the Church for the safe preservation of faith, or at least are proposed with authority.

4° From what has been said the various properties of faith are already known : on the part of the material object, infallibility and obscurity ; on the part of the will, freedom ; on the part of the judgment of credibility : reasonableness (and rational credibility of the object) ; on the part of the intellect adhering to the formal object, the highest certitude ; on the part of the external cause, God moving through grace : supernaturality ; on the part, finally, of the subject of faith there belongs irrevocability, as will be said below, n. 736, 3°.

729. Effects of faith. — Faith has as effects : 1° fear : inasmuch as by unformed faith we apprehend evils to be inflicted by divine judgment, it is the cause of servile fear, by which one fears to be punished by God ; inasmuch as by formed faith we esteem God as the Supreme Good, from which to be separated is the worst, and to be unwilling to be equal to which is evil, it is the cause of filial fear, by which one is subject to God and fears to be separated from God ; — 2° it has as effect the purification of the heart : for that is said to be impure which is mixed with baser things ; and that is purified which is mixed with nobler things. From which it is clear that a man becomes impure if he subjects himself with love to temporal things which are baser than himself ; but by faith he tends to things superior to himself, namely supernatural and divine things, and therefore faith is the principle of purification of the heart : unformed faith indeed purifies from error, which arises from the intellect's inordinate adherence to lower things ; formed faith also from the impurity of affection. Hence Acts XV, 9 : Faith purifying their hearts.