38 Something else I will say to my friends who marry and after long chastity and continence begin to burn and are as wanton as the brutes: “Are ye so foolish? Having begun in the Spirit, are you now perfected in the flesh? Did ye suffer so many things in vain?” If the Apostle in the case of some persons loosens the cords of continence, and lets them have a slack rein, he does so on account of the infirmity of the flesh. This is the enemy he has in view when he once more says: “Walk by the Spirit, and you shall not fulfill the lust of the flesh.
For the flesh lusts against the Spirit, and the Spirit against the flesh.” It is unnecessary now to speak of the works of the flesh: it would be tedious, and he who chooses can easily gather them from the letter of the Apostle. I will only speak of the Spirit and its fruits, love, joy, peace, long suffering, kindness, goodness, faithfulness, meekness, continence. All the virtues of the Spirit are supported and protected by continence, which is as it were their solid foundation and crowning point.
Against such there is no law. “And they that are of Christ have crucified their flesh with the passions and the lusts thereof. If we live by the Spirit, by the Spirit let us also walk.” Why do we who with Christ have crucified our flesh and its passions and desires again desire to do the things of the flesh? “Whatsoever a man sows, that shall he also reap. For he that sows unto his own flesh, shall of the flesh reap corruption; but he that sows unto the Spirit shall of the Spirit reap eternal life.”
I think that he who has a wife, so long as he reverts to the practice in question, that Satan may not tempt him, is sowing to the flesh and not to the Spirit. And he who sows to the flesh (the words are not mine, but the Apostle's) reaps corruption. God the Father chose us in Christ before the foundation of the world, that we might be holy and without spot before Him. We walked in the lusts of the flesh, doing the desires of the flesh and of the thoughts, and were children of wrath, even as the rest.
But now He has raised us up with Him, and made us to sit with Him in the heavenly places in Christ Jesus, that we may put away according to our former manner of life the old man, which is corrupt according to the lusts of deceit, and that blessing may be applied to us which so finely concludes the mystical Epistle to the Ephesians: “Grace be with all them that love our Lord Jesus Christ in uncorruptness.” “For our citizenship is in heaven; from whence also we wait for a Saviour, the Lord Jesus Christ: who shall fashion anew the body of our humiliation, that it may be conformed to the body of his glory. Whatsoever things then are true, whatsoever are chaste, whatsoever things are just, whatsoever things pertain to purity, let us join ourselves to these, let us follow these. Christ has reconciled us in his body to God the Father through his death, and has presented us holy and without spot, and without blame before himself: in whom we have been also circumcised, not with the circumcision made with hands, to the spoiling of the body of the flesh, but with the circumcision of Christ, having been buried with him in baptism, wherein also we rose with him. If then we have risen with Christ, let us seek those things which are above, where Christ sits on the right hand of God; let us set our affections on things above, not upon the things that are upon the earth. For we are dead, and our life is hid with Christ in God. When Christ our life shall appear, then we also shall appear with him in glory. No soldier on service entangles himself in the affairs of this life; that he may please him who enrolled him as a soldier. For the grace of God has appeared, bringing salvation to all men, instructing us, to the intent that, denying ungodliness and worldly lusts, we should live purely and righteously and godly in this present world.”
Source: Against Jovinianus (New Advent)