Today’s Catechism sections discuss mercy and the definition of sin. Supporting material comes from the “Summa Theologica”.

Article 8

SIN

I. Mercy and Sin

1846 The Gospel is the revelation in Jesus Christ of God's mercy to sinners.113 The angel announced to Joseph: "You shall call his name Jesus, for he will save his people from their sins."114 The same is true of the Eucharist, the sacrament of redemption: "This is my blood of the covenant, which is poured out for many for the forgiveness of sins."115

1847 "God created us without us: but he did not will to save us without us."116 To receive his mercy, we must admit our faults. "If we say we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just, and will forgive our sins and cleanse us from all unrighteousness."117

1848 As St. Paul affirms, "Where sin increased, grace abounded all the more."118 But to do its work grace must uncover sin so as to convert our hearts and bestow on us "righteousness to eternal life through Jesus Christ ourLord."119 Like a physician who probes the wound before treating it, God, by his Word and by his Spirit, casts a living light on sin:

Conversion requires convincing of sin; it includes the interior judgment of conscience, and this, being a proof of the action of the Spirit of truth in man's inmost being, becomes at the same time the start of a new grant of grace and love: "Receive the Holy Spirit." Thus in this "convincing concerning sin" we discover a double gift: the gift of the truth of conscience and the gift of the certainty of redemption. The Spirit of truth is the Consoler.120

II. The Definition of Sin

1849 Sin is an offense against reason, truth, and right conscience; it is failure in genuine love for God and neighbor caused by a perverse attachment to certain goods. It wounds the nature of man and injures human solidarity. It has been defined as "an utterance, a deed, or a desire contrary to the eternal law."121

1850 Sin is an offense against God: "Against you, you alone, have I sinned, and done that which is evil in your sight."122 Sin sets itself against God's love for us and turns our hearts away from it. Like the first sin, it is disobedience, a revolt against God through the will to become "like gods,"123 knowing and determining good and evil. Sin is thus "love of oneself even to contempt of God."124 In this proud self-exaltation, sin is diametrically opposed to the obedience of Jesus, which achieves our salvation.125

1851 It is precisely in the Passion, when the mercy of Christ is about to vanquish it, that sin most clearly manifests its violence and its many forms: unbelief, murderous hatred, shunning and mockery by the leaders and the people, Pilate's cowardice and the cruelty of the soldiers, Judas' betrayal - so bitter to Jesus, Peter's denial and the disciples' flight. However, at the very hour of darkness, the hour of the prince of this world,126 The sacrifice of Christ secretly becomes the source from which the forgiveness of our sins will pour forth inexhaustibly.

IN BRIEF

1870 "God has consigned all men to disobedience, that he may have mercy upon all" (⇒ Rom 11:32).

1871 Sin is an utterance, a deed, or a desire contrary to the eternal law (St. Augustine, Faust 22: PL 42, 418). It is an offense against God. It rises up against God in a disobedience contrary to the obedience of Christ.

1872 Sin is an act contrary to reason. It wounds man's nature and injures human solidarity.

In the “Summa Theologica” (Prima Secundæ Partis, 71, 6), St. Thomas Aquinas explores the definition of sin proposed by St. Augustine.

Article 6. Whether sin is fittingly defined as a word, deed, or desire contrary to the eternal law?

Objection 1. It would seem that sin is unfittingly defined by saying: "Sin is a word, deed, or desire, contrary to the eternal law." Because "Word," "deed," and "desire" imply an act; whereas not every sin implies an act, as stated above (Article 5). Therefore this definition does not include every sin.

Objection 2. Further, Augustine says (De Duab. Anim. xii): "Sin is the will to retain or obtain what justice forbids." Now will is comprised under desire, in so far as desire denotes any act of the appetite. Therefore it was enough to say: "Sin is a desire contrary to the eternal law," nor was there need to add "word" or "deed."

Objection 3. Further, sin apparently consists properly in aversion from the end: because good and evil are measured chiefly with regard to the end as explained above (1, 3; k1 18, A4,6; 20, A2,3): wherefore Augustine (De Lib. Arb. i) defines sin in reference to the end, by saying that "sin is nothing else than to neglect eternal things, and seek after temporal things": and again he says (Qq. lxxxii, qu. 30) that "all human wickedness consists in using what we should enjoy, and in enjoying what we should use." Now the definition is question contains no mention of aversion from our due end: therefore it is an insufficient definition of sin.

Objection 4. Further, a thing is said to be forbidden, because it is contrary to the law. Now not all sins are evil through being forbidden, but some are forbidden because they are evil. Therefore sin in general should not be defined as being against the law of God.

Objection 5. Further, a sin denotes a bad human act, as was explained above (Article 1). Now man's evil is to be against reason, as Dionysius states (Div. Nom. iv). Therefore it would have been better to say that sin is against reason than to say that it is contrary to the eternal law.

On the contrary, the authority of Augustine suffices (Contra Faust. xxii, 27).

I answer that, As was shown above (Article 1), sin is nothing else than a bad human act. Now that an act is a human act is due to its being voluntary, as stated above (Question 1, Article 1), whether it be voluntary, as being elicited by the will, e.g. to will or to choose, or as being commanded by the will, e.g. the exterior actions of speech or operation. Again, a human act is evil through lacking conformity with its due measure: and conformity of measure in a thing depends on a rule, from which if that thing depart, it is incommensurate. Now there are two rules of the human will: one is proximate and homogeneous, viz. the human reason; the other is the first rule, viz. the eternal law, which is God's reason, so to speak. Accordingly Augustine (Contra Faust. xxii, 27) includes two things in the definition of sin; one, pertaining to the substance of a human act, and which is the matter, so to speak, of sin, when he says "word," "deed," or "desire"; the other, pertaining to the nature of evil, and which is the form, as it were, of sin, when he says, "contrary to the eternal law."

Reply to Objection 1. Affirmation and negation are reduced to one same genus: e.g. in Divine things, begotten and unbegotten are reduced to the genus "relation," as Augustine states (De Trin. v, 6,7): and so "word" and "deed" denote equally what is said and what is not said, what is done and what is not done.

Reply to Objection 2. The first cause of sin is in the will, which commands all voluntary acts, in which alone is sin to be found: and hence it is that Augustine sometimes defines sin in reference to the will alone. But since external acts also pertain to the substance of sin, through being evil of themselves, as stated, it was necessary in defining sin to include something referring to external action.

Reply to Objection 3. The eternal law first and foremost directs man to his end, and in consequence, makes man to be well disposed in regard to things which are directed to the end: hence when he says, "contrary to the eternal law," he includes aversion from the end and all other forms of inordinateness.

Reply to Objection 4. When it is said that not every sin is evil through being forbidden, this must be understood of prohibition by positive law. If, however, the prohibition be referred to the natural law, which is contained primarily in the eternal law, but secondarily in the natural code of the human reason, then every sin is evil through being prohibited: since it is contrary to natural law, precisely because it is inordinate.

Reply to Objection 5. The theologian considers sin chiefly as an offense against God; and the moral philosopher, as something contrary to reason. Hence Augustine defines sin with reference to its being "contrary to the eternal law," more fittingly than with reference to its being contrary to reason; the more so, as the eternal law directs us in many things that surpass human reason, e.g. in matters of faith.

Footnotes

113 Cf. ⇒ Lk 15.
114 ⇒ Mt 1:21.
115 ⇒ Mt 26:28.
116 St. Augustine, Sermo 169, 11, 13: PL 38, 923.
117 1 Jn 8-9.
118 ⇒ Rom 5:20.
119 ⇒ Rom 5:21.
120 John Paul II, DeV 31 # 2.
121 St. Augustine, Contra Faustum 22: PL 42, 418; St. Thomas Aquinas, STh I-II, 71, 6.
122 ⇒ Ps 51:4.
123 ⇒ Gen 3:5.
124 St. Augustine, De civ. Dei 14, 28: PL 41, 436.
125 Cf. ⇒ Phil 2:6-9.
126 Cf. ⇒ Jn 14:30.