31 “But now do ye also,” says he, “put down all;” and he makes mention of several more evils of that sort. But what is it, that it is not enough for him to say, “Do ye put down all,” but that he added the conjunction and said, “ye also?” save that lest they should not think that they did those evils and lived in them with impunity on this account, because their faith set them free from wrath, which comes upon the sons of unbelief, doing these things, and living in them without faith.
Do ye also, says he, put down those evils, on account of which comes the wrath of God on the children of unbelief; nor promise yourselves impunity of them on account of merit of faith. But he would not say, “put ye down,” unto those who had already laid down so far as that they consented not to such faults, nor were yielding their members to them as weapons of sin, save that the life of Saints stands in this past deed, and is still engaged in this work, so long as we are mortal.
For, so long as the Spirit lusts against the flesh, this business proceeds with great earnestness, resistance is offered unto evil delights, unclean lusts, carnal and shameful motions, by the sweetness of holiness, by the love of chastity, by spiritual vigor, and by the beauty of continence; thus they are laid down by them who are dead to them, and who live not in them by consenting. Thus, I say, they are put down, while they are weighed down by continued continence, that they rise not again.
Whosoever, as though secure, shall cease from this laying aside of them, straightway they will assault the Citadel of the mind, and will themselves put it down thence, and will reduce it into slavery to them, captive after a base and unseemly fashion. Then sin will reign in the mortal body of man to obey its desires; then will it yield its members weapons of unrighteousness unto sin: and the last state of that man shall be worse than the former. For it is much more tolerable not to have begun a contest of this kind, than after one has begun to have left the conflict, and to have become in place of a good warrior, or even in place of a conqueror, a captive. Whence the Lord says not, whoso shall begin, but “Whoso shall persevere unto the end, he shall be saved.”
Source: On Continence (New Advent)