Thomas Aquinas, on Gal 5:19

“Now the works of the flesh are manifest, which are fornication, uncleanness, immodesty, luxury,”

“Then when he says, "the works of the flesh are manifest," he proves what he has said through certain effects. First, he mentions the works of the flesh which are opposed to the Holy Spirit; Secondly, he shows how the works of the Spirit are not forbidden by the Law (23b). As to the first, he does two things: First, he mentions the works of the flesh that are forbidden by the Law; Secondly, the works of the Spirit which are not forbidden by it (v. 22). As to the first, he does two things: First, he enumerates the works of the flesh; Secondly, he mentions the harm that follows from them (v. 21). With respect to the first, two doubts arise. First, as to the Apostle's mentioning things that do not pertain to the flesh, but which he says are works of the flesh, such as idolatry, sects, emulations, and the like. I answer that, according to Augustine in The City of God (Bk. 14), he lives according to the flesh who lives according to himself. Hence flesh is taken here as referring to the whole man. Accordingly, whatever springs from disordered self-love is called a work of the flesh. Or, one should say that a sin can be called "of the flesh" in two ways: namely, with respect to fulfillment, and in this sense only those are sins of the flesh that are fulfilled in the pleasure of the flesh, namely, lust and gluttony; or with respect to their root, and in this sense all sins are called sins of the flesh, inasmuch as the soul is so weighed down by the weakness of the flesh (as is written in Wisdom 9:15) that the enfeebled intellect can be easily misled and hindered from operating perfectly. As a consequence, certain vices follow therefrom, namely, heresies, sects and the like. In this way it is said that the "fomes" is the source of all sins. The second doubt is that, since the Apostle says that "they who do such things shall not obtain the kingdom of God," whereas no one is excluded from the kingdom of God except for mortal sin, it follows that all the sins enumerated are mortal sins. But the contrary seems to be the case, because in this list he enumerates many that are not mortal sins, such as contention, emulation, and the like. I answer that all the sins listed here are mortal one way or another: some are so according to their genus, as murder, fornication, idolatry, and the like; but others are mortal with respect to fulfillment, as anger, whose fulfillment consists in harm to neighbor. Hence if one consents to that harm, there is mortal sin. In like manner, eating is directed to the pleasure of food, but if one places his end in such pleasures, he sins mortally; accordingly, he does not say "eating" but revellings. And the same must be said of the others that are like this. Thirdly, there is a doubt about the order followed in this list. However, it should be recognized that when the Apostle varies his enumeration of various vices in various texts, it is not his intention to enumerate all the vices in perfect order and according to the rules of the art, but only those in which the persons to whom he is writing abound and in which they are excessive. Therefore in these lists one should look not for completeness but for the cause of the variation. Having settled these doubts, we should next observe that the Apostle lists certain vices of the flesh that concern things not necessary to life and others that concern things necessary to life. As to the first, he mentions certain vices that a man commits against himself; then those that are against God; finally, those that are against the neighbor. Against the self are four. These he mentions first, because they obviously spring from the flesh. Two of these pertain to the carnal act of lust, namely, "fornication," when an unmarried man becomes one with an unmarried woman with respect to the natural use of lust. The other is "uncleanness" as to a use which is contrary to nature—"No fornicator or unclean... hath inheritance in the kingdom of Christ and of God" (Eph 5:5); "They have not done penance for the uncleanness and fornication and lasciviousness that they have committed" (2 Cor 12:21). The other two are ordained to the aforesaid acts: one is performed outwardly, as touches, looks, kisses and the like; as to these he says, "immodesty": "Who despairing, have given themselves up to immodesty unto the working of all uncleanness" (Eph 4:19). The other inwardly, namely, unclean thoughts; as to this he says, "luxury": "When they have grown wanton in Christ, they will marry" (1 Tim 5:11).”

Imported from an open dataset — not yet checked against the printed edition.