The attempt to understand mysteries or to establish them by natural reason is opposed to the humble assent of faith: “He that is a searcher of majesty, shall be overwhelmed by glory” (Prov., xxv. 27); “Seek not the things that are too high for thee, and search not into things above thy ability” (Ecclus., iii. 22); “Faith loses its merit, if it is put to the test of reason” (St. Gregory the Great, Hom. xxvi).
796. Besides the internal act of acceptance of revealed truth, faith has also external acts. (a) It commands the external acts of the other virtues, that is, acts directed to the specific ends of those virtues. Hence, one who fasts exercises an external act of the virtue of temperance, but it is his faith in the virtue that commands the fast. (b) Faith elicits the external act of profession of faith as its own proper external act directed to its own specific end: “I believed, for which cause I have spoken” (Ps. cxv. 10; II Cor., iv. 13). External profession of faith, therefore, is not an act proceeding from faith; it is an act of faith. The necessity of this act will be considered below in the article about the commandments of faith.
797. The Habit of Faith.—Faith is not only an act that passes, but it is also a permanent quality or habit conferred by God, one of the “most great and perfect promises” which man must make use of (II Peter, i. 3 sqq.), a charism that is not for a time but for all this life, just like hope and charity (I Cor., xiii. 13). God, who does all things sweetly (Wis., viii. 1), and who has provided for His natural creatures internal powers by which they incline and move themselves towards the ends of their activities, has not done less for those whom He moves to a supernatural destiny; and, in justifying the sinner, He infuses along with grace the supernatural virtues of faith, hope and charity (Council of Trent, Sess. VI, Cap. 6).
798. The virtue of faith is thus defined by the Council of the Vatican: “Faith is a supernatural virtue, by which, with the help of God’s grace, we believe the truths revealed by Him, not on account of an intrinsic evidence of the truths themselves, perceived by natural reason, but on account of the authority of God who revealed them.”
799. Hence, the virtue of faith has the following properties:
(a) It is supernatural, not only because its object and motive are supernatural, but because it proceeds from a supernatural principle, i.e., grace (John, vi, 29; Eph., ii. 8).
(b) It is obscure, because the believer assents to that which has no intrinsic evidence for him. He does not see its truth as the blessed see God, for “we see now through a glass in a dark manner, but then face to face” (I Cor., xiii. 12). He does not know its truth as he knows evident or naturally demonstrated propositions, for faith is about truths that surpass reason—things “that appear not.” This, of course, does not mean that faith is not rightly called a new light added to the mind, and that the motives which call for the acceptance of faith are not evidently credible.
(c) It is free, because, although one cannot dissent from that which is evident intrinsically (e.g., that two and two make four), one is able to dissent from that which is obscure.
(d) It is not a process of reasoning, but a simple act of assent, in which one accepts at the same time the authority of the Revealer and the truth of His revelation. “Jesus said to her (Martha): I am the resurrection and the life .... Believest thou this? She saith to Him: Yea, Lord, I have believed that Thou art the Christ, etc.” (John, xi. 25-27).
(e) It is firm and unshaken in a far higher degree than the assent of understanding and science, since it rests on the infallible authority of God (I Thess., ii. 13).