Objection 1. It would seem that no movement of faith is required for the justification of the ungodly. For as a man is justified by faith, so also by other things, viz. by fear, of which it is written (Sirach 1:27): "The fear of the Lord driveth out sin, for he that is without fear cannot be justified"; and again by charity, according to Luke 7:47: "Many sins are forgiven her because she hath loved much"; and again by humility, according to James 4:6: "God resisteth the proud and giveth grace to the humble"; and again by mercy, according to Proverbs 15:27: "By mercy and faith sins are purged away." Hence the movement of faith is no more required for the justification of the ungodly, than the movements of the aforesaid virtues.
Objection 2. Further, the act of faith is required for justification only inasmuch as a man knows God by faith. But a man may know God in other ways, viz. by natural knowledge, and by the gift of wisdom. Hence no act of faith is required for the justification of the ungodly.
Objection 3. Further, there are several articles of faith. Therefore if the act of faith is required for the justification of the ungodly, it would seem that a man ought to think on every article of faith when he is first justified. But this seems inconvenient, since such thought would require a long delay of time. Hence it seems that an act of faith is not required for the justification of the ungodly.
On the contrary, It is written (Romans 5:1): "Being justified therefore by faith, let us have peace with God."
I answer that, As stated above (Article 3) a movement of free-will is required for the justification of the ungodly, inasmuch as man's mind is moved by God. Now God moves man's soul by turning it to Himself according to Psalm 84:7 (Septuagint): "Thou wilt turn us, O God, and bring us to life." Hence for the justification of the ungodly a movement of the mind is required, by which it is turned to God. Now the first turning to God is by faith, according to Hebrews 11:6: "He that cometh to God must believe that He is." Hence a movement of faith is required for the justification of the ungodly.
Reply to Objection 1. The movement of faith is not perfect unless it is quickened by charity; hence in the justification of the ungodly, a movement of charity is infused together with the movement of faith. Now free-will is moved to God by being subject to Him; hence an act of filial fear and an act of humility also concur. For it may happen that one and the same act of free-will springs from different virtues, when one commands and another is commanded, inasmuch as the act may be ordained to various ends. But the act of mercy counteracts sin either by way of satisfying for it, and thus it follows justification; or by way of preparation, inasmuch as the merciful obtain mercy; and thus it can either precede justification, or concur with the other virtues towards justification, inasmuch as mercy is included in the love of our neighbor.
Reply to Objection 2. By natural knowledge a man is not turned to God, according as He is the object of beatitude and the cause of justification. Hence such knowledge does not suffice for justification. But the gift of wisdom presupposes the knowledge of faith, as stated above (68, 4, ad 3).
Reply to Objection 3. As the Apostle says (Romans 4:5), "to him that... believeth in Him that justifieth the ungodly his faith is reputed to justice, according to the purpose of the grace of God." Hence it is clear that in the justification of the ungodly an act of faith is required in order that a man may believe that God justifies man through the mystery of Christ.
Source: Summa Theologica (New Advent)