1. Certain sins, such as idolatry, obviously infringe upon religion, but it is not so clear what bearing most immoral acts have upon the relationship with God. How do immoral acts which do not directly involve religion nevertheless offend God?
2. St. Augustine defines sin as “anything done, said, or desired against the eternal law” (FEF 1605). The eternal law is God’s wise plan by which he directs all things to their fulfillment: integral human fulfillment, in our case. Every immoral act, however, involves lack of openness to integral human fulfillment. Thus, one who acts immorally always deviates from the loving plan of the eternal law, regardless of which particular human good is directly at stake (see S.t., 1–2, q. 71, a. 2, ad 4; a. 6). This can be seen more clearly if one considers the various ways in which people know what is right.
3. The people of the old covenant and we of the new accept God in faith as our Lord. It is his plan and will that we should worship him alone, for other worship is senseless and degrading; that we should treat one another as persons made in his image and called to share in his life; that we should be liberated from self-imposed limitations and brought to share in Jesus’ glory. Whenever the law of Moses forbade something, the pious Jew knew it to be against God’s wisdom and love; similarly, when the Church teaches that something is a sin, the faithful Catholic knows it to be against God’s wisdom and love. Every immoral act deviates from God’s plan for our fulfillment. In doing so, it also violates covenant friendship with God, for as part of this covenant relationship he wishes us to cooperate in carrying out his plan. But violation of friendship with God alienates us from him, and such alienation is sin. Therefore, every immoral act is sin.
4. However, even the pagans, although not within the covenant, know what is right and are capable of sin (see Rom 1.18–22). For even without faith, people can realize that immorality offends not only against reason and, often, the rights of one’s neighbor but also against the more-than-human source of meaning and value called “God.” One who violates moral requirements refuses to accept his or her limitation as a creature and implicitly aspires to be beyond boundaries, as God is.5 Thus, in sinning, one implicitly rejects God’s wisdom and love, the source of meaning and value in creation at large and in human life in particular. But those who reject God’s wisdom and love in effect declare their independence of God and so alienate themselves from him. This alienation, implicit in every immoral act, is sin.
5. An unreasonable, morally evil act can be recognized as sin in two ways, for there are two distinct routes by which we know immorality to be against God’s mind and will. First, in acting against a conscience formed in the light of faith, one violates the covenant of faith and so violates the eternal law which faith makes known. In other words, when one offends against the Church’s teaching, one offends against the divine truth of the gospel, which is the source of the Church’s teaching. Second, in violating one’s conscience, one violates natural law and so violates the eternal law in which natural law participates (see 7‑A). In other words, in violating human reason, one violates the light of divine wisdom which shines there. When they act immorally, Christians are more or less clearly aware in both of these ways of sinning.
Noticing the first way in which sin is against the eternal law and mistakenly thinking it to be the only possible way to relate moral evil to God’s plan, some have taught that there is a real distinction between “theological sin” and “philosophical sin.” Theological sin, on their account, is a deliberate transgression of God’s law, done by one who is aware of God and conscious of the fact that the act is a violation of his will. Philosophical sin is a morally evil act done by one who does not know God or is not thinking about him—the immorality, for instance, of a pagan who does not know God or a Christian who knows that something is wrong but has never heard that this kind of act is a mortal sin. Those who held this view wished to deny that “philosophical sin” could be mortal. The Church firmly condemns this position (see DS 2291/1290).
6. If Christians commit mortal sins, their offenses are worse than those of nonbelievers. To sin after receiving the truth is infidelity, as the prophets, especially Hosea, make clear. In the old law, infidelity was punishable by death. “How much worse punishment do you think will be deserved by the man who has spurned the Son of God, and profaned the blood of the covenant by which he was sanctified, and outraged the Spirit of grace?” (Heb 10.29). In sinning gravely, Christians exchange the life and liberty won for them by Jesus for renewed death and slavery (see Rom 6; Gal 5). Since the Christian is a member of Christ’s body and a temple of the Spirit, a sin such as fornication takes on the character of sacrilege (see 1 Cor 6.12–20). And since Christian life is not merely individual, every grave sin violates a Christian’s responsibility to Christ and the Church (see Rom 14.7–8; Gal 5.13–6.10). (The last point will be developed in 16‑G.)
7. Since we determine ourselves by our choices and these last, in sinning more gravely than nonbelievers Christians also harm themselves more radically. Even though not chosen as a good, sin’s offensiveness to God and injuriousness to the Church, which a Christian willingly accepts in committing grave sin, affect his or her very being unless and until the sin is repented and forgiven. Therefore, “If, after they have escaped the defilements of the world through the knowledge of our Lord and Savior Jesus Christ, they are again entangled in them and overpowered, the last state has become worse for them than the first. For it would have been better for them never to have known the way of righteousness than after knowing it to turn back from the holy commandment delivered to them” (2 Pt 2.20–21).
8. St. Augustine tries to clarify how sin offends against God by saying that in every immoral act one turns from God to a creature and loves oneself to the point of contempt for God (see appendix 1). These things—turning from God and contempt for God—can be understood in terms of the implications of moral evil which have already been explained. One who refuses to follow God’s wise guidance in the matter of true human fulfillment does turn from him and contemptuously prefers his or her own arbitrary satisfaction to the full good proposed by God’s love.
9. Still, St. Augustine’s clarification of sin as a turning away from God and contempt for him is easily misunderstood. This happens, for instance, if it is supposed that one does not sin unless one purposely offends God (cf. S.t., 3, q. 88, a. 4). In fact, however, sinners generally do not advert to the fact that their sins are offenses against God or, if they are believers, only reluctantly accept this implication of their sinning.
10. Augustine’s clarification is also misunderstood if taken to mean that the nonreligious aspects of sin are in themselves unimportant and only the offense against God is evil. On the contrary, the self-mutilation involved in sin, its social implications, and its incompatibility with integral human fulfillment are of themselves important aspects of its evil. It is because immorality does involve these evils that God’s commandments are not arbitrary restrictions on our freedom but wise and loving guides directing us toward true human fulfillment.
The self constituted by immoral choices is insubstantial; it is the “I” in search of its own emotional peace, security, success, and satisfaction—in short, it is the sinful self St. Augustine so well analyzed. This is the self which Jesus teaches one must lose to find one’s true self (see Mt 16.24; Mk 8.34; Lk 9.23). Therefore, in this sense of “self-love,” all sin is perverse self-love, for it is the pursuit of a “me” defined by sinful passion, not the pursuit of the “we” in which divine and human persons will be united in the fulfillment of all things in Jesus.
5. Lyonnet and Sabourin, op. cit., 5.