^6:12 Let not sin therefore reign in your mortal body, so as to obey the lusts thereof. [n. 492]
^6:13 Neither yield your members as instruments of iniquity unto sin: but yield yourselves to God, as those that are alive from the dead; and your members as instruments of justice unto God.
^6:14 For sin shall not have dominion over you: for you are not under the law, but under grace. [n. 496]
^6:15 What then? Shall we sin, because we are not under the law, but under grace? God forbid! [n. 499]
^6:16 Know you not that to whom you yield yourselves servants to obey, his servants you are whom you obey, whether it be of sin unto death or of obedience unto justice.
^6:17 But thanks be to God, that you were the servants of sin but have obeyed from the heart unto that form of doctrine into which you have been delivered.
^6:18 Being then freed from sin, we have been made servants of justice.

492. After showing that we ought not remain in sin and that we have the faculty for this, the Apostle concludes with a moral exhortation.

And concerning this he does three things:

first, he proposes an admonition;

second, he assigns a reason, at for sin shall not;

third, he raises and solves a question, at what then? Shall we sin.

In regard to the first he does two things:

first, he proposes the admonition;

second, he clarifies it, at so as to obey.

493. First, therefore, he says: we have said that our old self was crucified once, so that the body of sin may be destroyed. This means that the power of sin has been so weakened that it cannot rule us. Let not sin therefore reign in your mortal body any longer.

He does not say: let not sin be in your mortal body, because as long as our body is mortal, i.e., bound to the necessity of death, it is not possible for sin not to be in our body, i.e., the inclination to sin. But since we have been freed from the kingdom of sin by God, we must struggle in order that sin not recover its dominion now lost in our body. And this is what he says: let not sin reign in your mortal body. This is something about which one must be on his guard, as long as we wear the mortal body: the corruptible body is a load upon the soul (Wis 9:15).

494. Then when he says, so as to obey, he clarifies this admonition.

In regard to this it should be noted that sin reigns in man in two ways: in one way, through internal consent of the mind. To remove this he says, so as to obey the lusts thereof. For it is by obeying the passions of sin with our minds that sin reigns in us: go not after your lusts (Sir 18:30).

In a second way sin reigns in us through the performance of the act. To exclude this, he adds, neither yield your members unto sin, i.e., to the inclination to sin, as instruments of iniquity, i.e., as instruments for committing sin. For when man commits sin through his members, he yields to sin. In this way he seems to fight to restore sin’s dominion, which grows in us through the habit of sinning: they went down to hell with their weapons (Exod 32:27).

495. Then when he says, but yield yourselves to God, he urges them to the opposite, namely, to yield themselves to God.

And first with regard to the internal faculties when he says, but yield yourselves to God by submitting your mind to God: and now, Israel, what does the Lord your God require of you but that you fear the Lord your God and walk in his ways (Deut 10:12). And you ought to do this as those that are alive from the dead, i.e., as led from the death of sin to the life of grace. Hence it is fitting, since he died for all, that those who live might no longer live for themselves but for him who for their sake died and was raised (2 Cor 3:15).

Second, with respect to outward actions; hence he says, yield your members . . . unto God, i.e., to his service, as instruments of justice with which to fight against God’s enemies: put on the whole armor of God, that you may be able to stand against the wiles of the devil (Eph 6:11).

496. Then when he says, for sin shall not, he assigns the reason for this admonition.

For someone might excuse himself, alleging that sin’s dominion is an obstacle to obeying the admonition. But the Apostle excludes this, saying, for sin shall not have dominion over you, i.e., if you begin to resist sin and yield yourself to God: draw near to God and he will draw near to you. Resist the devil and he will flee from you (Jas 4:8). As if to say: you can observe my admonition, because you do not find sin dominating and holding you. For we have been freed by Christ, as John says: if the Son makes you free, you will be free indeed (John 8:36).

497. Then he clarifies what he had said, saying, for you are not under the law, but under grace.

Here it should be noted that he is not speaking of the law merely with respect to its ceremonial precepts, but even with respect to moral matters. For one is said to be under the law in two ways.

In one way, as voluntarily subject to the observance of the law. Even Christ was under the law in this way according to Galatians: born under the law (Gal 4:4), namely, because he observed the law, not only the moral but also the ceremonial precepts. But the faithful of Christ are under the law in this way, with respect to the moral precepts but not the ceremonial.

In another way, one is said to be under the law as though compelled by the law. In this way, one is under the law when he does not obey it voluntarily from love but is compelled by fear. But such a one lacks grace which, if it were present, would incline the will to observe the law and fulfill its moral precepts from a motive of love. Therefore, as long as one is under the law in such a way that he does not fulfill it voluntarily, sin has dominion over him. As a result, such a man’s will is inclined to choose what is contrary to the law. But through grace such dominion is removed; consequently, a man observes the law not as existing under the law but as free: we are not children of the slave but of the free woman, by the freedom with which Christ has set us free (Gal 4:31).

498. This grace, making men freely obey the law, was not conferred by the sacraments of the old law, but Christ’s sacraments conferred it. Consequently, those who submitted themselves to the ceremonies of the law were not, so far as the power of those sacraments was concerned, under grace but under the law, unless they happened to obtain grace through faith. But one who submits to Christ’s sacraments obtains grace from his power, so as not to be under the law but under grace, unless they enslaved themselves to sin through their own fault.

499. Then when he says, what then, he raises a question against what he has said.

And concerning this he does three things:

first, he raises the question;

second, he answers it, at God forbid! Know you not;

third, he shows how unfitting it would be to misinterpret his statement, at but thanks be to God.

500. In regard to the first it should be noted that his statement could be falsely interpreted, namely, that Christ’s faithful are not under the law with respect to being obliged to obey its moral precepts. For it would follow that Christ’s faithful could lawfully commit sin and act against the moral precepts.

Therefore, in this context he raises the question: what then? Shall we sin, i.e., shall we act against the moral precepts, because, as has been said, we are not under the law, but under grace? This interpretation the Apostle rejects in Galatians: for you were called to freedom, brethren, only do not use your freedom as an opportunity for the flesh (Gal 5:13).

501. In the same fashion he answers here, God forbid that we should sin, because we have been set free from the law; because if we were to sin, we would once more be reduced to the slavery of sin.

Hence, he continues, know you not that to whom you yield yourselves of your own will as servants to obey voluntarily, his servants you are whom you obey. For obedience is a debt which slaves owe to their masters: slaves, be obedient to your earthly masters (Eph 6:5). Hence, when someone obeys another, he admits that he is his slave by obeying. But different masters are obeyed for different remunerations. For the one who obeys sin is led to death through the slavery of sin. And this is what he says: whether it be of sin, i.e., you are its slaves by obeying it, unto death, i.e., to the eternal damnation of the one who falls. Concerning this death it is said: he who conquers shall not be hurt by the second death (Rev 2:11). But the one who obeys God is made a slave of this obedience, because through the habit of obeying the mind is inclined more and more to obeying and as a result achieves holiness. Therefore, he says: or of obedience, namely, of the divine precepts, unto justice: the doers of the law shall be justified (Rom 2:13).

Sin and obedience are fittingly presented as opposites, because, as Ambrose says, sin is a transgression of the divine law and a disobedience against the heavenly commands.

502. Then when he says, but thanks be to God, he shows the folly of obeying sin and thereby returning to the slavery of sin: first, by considering the benefit we have received. For if someone, by another’s graciousness is freed from slavery, it is unfitting to subject oneself freely to slavery. Hence, since we have been freed from sin by the grace of God, it is unfitting willfully to return again to the slavery of sin.

Second, by considering the state into which we were led after freedom from sin, namely, that we are slaves to justice. But, it is not lawful for a slave to subject himself to the dominion of an opposite master; hence, it is not lawful, if we have been made slaves of justice, to return to the slavery of sin.

503. The Apostle touches on both of these considerations, when he says: I thank God, and you too should thank God, that you were the servants of sin, because he who commits sin, is a servant of sin (John 8:34), but have obeyed, namely, by believing: for obedience to the faith, in all nations (Rom 1:5); and this not as though compelled, but from the heart: for with the heart, we believe unto justice (Rom 10:10), unto that form of doctrine, i.e., to the doctrine of the Catholic faith: follow the pattern of the sound words you have heard from me (2 Tim 1:13), into which you have been delivered: i.e., gave yourselves entirely: but first they gave themselves to the Lord and to us by the will of God (2 Cor 8:5). And by this being then freed from sin, so that it is not fitting to desert justice: you were bought with a price (1 Cor 7:23) and are not your own.