1. In making an act of living faith (that is, faith motivated by love of God), one makes a free choice to accept God’s personal communication (see S.t., 2–2, q. 4, aa. 3–5; cf. q. 2, aa. 3, 9). This choice is made for the sake of the human goods of truth and religion. By the commitment of faith, one causes oneself to share in the human goods of the Christian community. The act of faith also contributes intrinsically to constituting, from the believer’s side, the intimate relationship with God.
In living faith one makes a human free choice to accept God’s proposal of intimate communion. Those who accept Jesus are given “power to become children of God” (Jn 1.12). St. John Chrysostom comments that the power is like that given an authorized agent, and that it is received in baptism. If one uses this power properly, then with the grace of God one has it in one’s own free will to become a child of God.12 The first Christian act of an adult who is being baptized is the act of living faith which those seeking baptism ask of the Church (see DS 1531/800).13
By any commitment one makes oneself be a person of definite identity, for free choice is self-determination. As a human free choice made for the sake of the human goods of truth and religion, a person’s commitment of faith is likewise self-determining. Thus, by this human free choice, one makes oneself share in the human goods of Christian community, such as religion and truth—for example, one becomes a catechumen, associates with members of the Church, participates in some of their religious acts, such as prayers, and receives instruction in the faith.
Now, in the act of living faith, one’s acceptance of God’s proposal is transformed by being made out of love of him. The transformation occurs by God’s gift, the love poured forth in our hearts through the Holy Spirit, and not by a self-creative act of our own. Thus we participate in divinity by our own free choice—not, however, by constituting ourselves divine, but by God’s so constituting us (see S.t., 1–2, q. 113, aa. 3–4). The act of living faith is the fundamental commitment of Christian life, the first act which is both divine and human in one who is drawn into and enters adoptive divine childhood by this very act. Since this act is primary, its make up is the matrix and paradigm for every other act of Christian life.
2. To understand the role of human goods in the act of faith it is necessary to bear in mind that any human choice whatsoever is directed to some basic human good. The Council of Trent teaches that, prior to living faith, a person prepares for it with God’s help by listening to the gospel proclaimed by the Church, recognizing the Church’s credibility, and believing it with a human credence (see DS 1526/798, 1530/800). In this way, as Vatican I expressly teaches, the acceptance of God in faith is a reasonable, free human act (see DS 3009–10/1790–91, 3033/1812). Such an act of reasonable submission, which is not suspended when the gift of faith is received, is directed to the human goods of truth and religion. Thus, converts come to the Church and seek faith from her in baptism because they think her teaching true and her way of life a sound path to peace with God. These are the same general goods sought more or less adequately by every religious person.
3. The content of faith includes many propositions which are not evident and seem false to nonbelievers. The factors making it possible to give responsible assent to these are twofold. First, because human relationships in general depend so heavily on faith, it is universally accepted that testimony ought to be believed, provided the one offering it seems competent and honest. This general norm of believing grounds a cautious receptivity and open-mindedness on the part of an upright person toward the gospel. Second, when carried out as it should be, the preaching of the gospel is accompanied by signs sufficient to show that, despite its extraordinary content, those who proclaim it are sincere and qualified in the field of religious truth, that is, the truth concerning humankind’s relationship with God. Thus the hearer has good reason to believe but still has a choice, and so believes freely (see S.t., 2–2, q. 2, a. 1, ad 1, 3; a. 9, ad 2, 3).
There are provisional grounds of faith which finally matures into absolute acceptance of God’s self-revelation (see Mk 8.22–26; Jn 4.6–42). Jesus normally did signs in response to an incipient faith, and by means of these signs elicited faith in his revelation. Faith is given to provide eyes to see and ears to hear if one is willing to accept it (see Mt 16.5–12). But no cogent sign is offered to the closed-minded who are not prepared to receive God’s saving love (see Mt 16.1–4; Lk 12.54–56). Confronted with facts, people do not automatically believe in the relevant way (see Mk 16.11–14; Lk 24.11, 37, 41).
4. The obligation to believe existed from the beginning of the human race. The very relationship of creature to creator is enough to require assent as soon as it is clear that one is being approached by God. Furthermore, as Vatican II teaches, God’s love in creating implies a call for human response: “From the very circumstance of his origin, man is already invited to converse with God” (GS 19). Even by the light of natural reason human beings can know themselves to be creatures (see DS 3004/1785). They should admit this truth and live by it.
5. In sum, every human person has a duty of conscience to seek the truth, especially religious truth, and embrace it when found (see DH 2, 10). Given the gospel’s message and the evidence of its credibility, a reasonable person ought to accept its truth. Yet the truth of faith is not evident; one can refuse to assent and one’s choice to assent remains free (see DS 1525/797, 1554/814). Thus, a person makes an act of faith as a personal commitment by choosing in accord with an upright conscience to accept the gospel’s message. In accepting the gospel, one makes the fundamental option to be a Christian.
6. To refuse to believe is a sin. The only reason for this sin is a pre-existing state of sin. The explanation of the parable of the sower (see Mk 4.13–20) suggests that whether revelation is received and flourishes depends on the antecedent dispositions of the recipient. St. John makes the same point more bluntly: Those whose deeds are wicked love darkness, while those who act in truth come into the light and believe in Jesus (see Jn 3.17–21).
The explanation for unbelief is clear and it is simple: Sin and rationalization block openness to God’s truth. “For every one who does evil hates the light, and does not come to the light, lest his deeds should be exposed. But he who does what is true comes to the light, that it may be clearly seen that his deeds have been wrought in God” (Jn 3.20–21). One who sins does not love himself or herself properly, and so cannot remain open to infinite goodness of which one’s own goodness is a participation (see S.t., 2–2, q. 25, a. 7). Those who oppose Jesus are willfully blind to the truth (see Jn 9.39–41). Faith is demanding. One who loves God is going to keep his commandments (see Mt 19.16–21; Jn 15.10). One unwilling to keep the commandments will be unable to believe, for that would mean doing God’s will.
7. God’s word is an indestructible seed. Unlike human things, which can be lost or destroyed, it stands firm (see 1 Pt 1.23–25). Hence, once we have received faith, it will not be taken away from us. We will remain partners of Jesus as long as we do not rebel against the truth accepted in faith (see 2 Tm 2.11–13). Unfortunately, though, “By rejecting conscience, certain persons have made shipwreck of their faith” (1 Tm 1.19). But that is a very different thing from “losing” one’s faith, if this means simply suffering such a loss, without any fault on one’s own part.
8. Since, as Vatican I teaches, God “strengthens with his grace those whom he has brought out of darkness into his marvelous light (see 1 Pt 2.9), so that they may remain in this light,” those who have accepted the faith under the teaching authority of the Church “can never have any just reason for changing that faith or calling it into doubt” (DS 3014/1794; translation amended; cf. DS 3036/1815). To deny this is to reject not only Vatican I but the Council’s premise: that God is faithful and never abandons anyone unless that person first abandons him (see DS 3014/1794, 1537/804).
The very fact that faith is personal acceptance of God excludes one from picking and choosing among the truths of faith, obeying some of its demands while disregarding others. God’s truth is one and his will is one. We receive his one truth in many doctrines and moral norms. Assuming the usual conditions of responsibility (reflection and consent) are met, to deny any one doctrine or moral norm—to deny, not merely to violate—is to make a commitment incompatible with faith. One can continue to think one has faith; one can continue to behave in many respects like a good Catholic; one will be counted as a Catholic by those who take polls. But one has become an infidel, and this has happened not by loss of faith, but by unfaithfulness to God (see S.t., 2–2, q. 5, a. 3; q. 11, aa. 1–2).
12. St. John Chrysostom, Commentary on Saint John the Apostle and Evangelist: Homilies 1–47, trans., Sr. Thomas Aquinas Goggin, S.C.H. (New York: Fathers of the Church, 1957), 100–101 (homily 10).
13. See The Rite of Christian Initiation of Adults, sec. 75. A theological account of faith as a human act: Benoît Duroux, O.P., La psychologie de la foi chez saint Thomas d’Aquin (Paris: Téqui, 1977).