9 And also, when he exhorts us, that we live not after the flesh, lest we die, but that by the Spirit we mortify the deeds of the flesh, that we may live; surely the trumpet which sounds, shows the war in which we are engaged, and enkindles us to contend keenly, and to do our enemies to death, that we be not done to death by them. But who those enemies are, it has set forth plainly enough. For those are they, whom it willed should be done to death by us, that is to say, the works of the flesh.
For so it says, “But if by the Spirit you shall mortify the deeds of the flesh, you shall live.” And in order that we may know what these are, let us hear the same in like manner writing unto the Galatians, and saying, “But the works of the flesh are manifest, which are, fornications, uncleannesses, luxuries, idolatry, witchcrafts, hatreds, contentions, emulations, wraths, strifes, heresies, envyings, drunkennesses, revellings, and such like; of which I foretell to you, as I have foretold, that they who do such things shall not possess the kingdom of God.” For the very war there also was he showing, that he should speak of these, and unto the death-doing of these enemies was he calling up the soldiers of Christ by the same heavenly and spiritual trumpet.
For he had said above, “But I say, walk in the Spirit, and perform ye not the lusts of the flesh. For the flesh lusts against the Spirit, and the Spirit against the flesh. For these are opposed one to the other, that you do not what ye would. But if you are led by the Spirit, you are not under the Law.” Therefore being set under Grace, he would have them have that conflict against the works of the flesh. And in order to point out these works of the flesh, he added what I have mentioned above.
“But the works of the flesh are manifest, which are, fornications,” and the rest, whether what he mentioned, or whether what he admonished were to be understood, chiefly as he added, “and such like.” Lastly, in this battle, against what is in a manner the carnal army leading forth as it were another spiritual line, “But the fruit of the Spirit is,” says he, “charity, joy, peace, long-suffering, kindness, goodness, faith, gentleness, continence; against such there is no law.” He says not “against these,” lest they should be thought to be alone: although even were he to say this, we ought to understand all, whatever goods of the same kind we could think of: but he says, “against such,” that is to say, both these and whatsoever are such like.
However, in that among the goods of which he made mention, he set Continence in the last place, (concerning which we have now undertaken to treat, and on account of which we have already said much,) he willed that it should in a special manner cleave to our minds. Forsooth this same is of great avail in this case, wherein the Spirit lusts against the flesh; forasmuch as in a certain way it crucifies the lusts of the flesh. Whence, after the Apostle had thus spoken, he added straightway, “But they who are Jesus Christ's have crucified their own flesh, with the passions and lusts.” This is the acting of Continence: thus the works of the flesh are done to death. But they do to death those, whom falling away from Continence lust draws into consent to do such works.
Source: On Continence (New Advent)