According to St. John Cassian, those who are married must embrace the spiritual disciplines that foster chastity; for many are not lovers of marriage but slaves of lust. Marriage in and of itself is not a cure of the passions and spouses who neglect the spiritual life may endlessly continue in the struggle against themselves for purity of heart. Within them may remain the conflict between sexual habit and continence of heart. In many ways sexuality is a perfect mirror of the human self and a lens through which we see the contortions and distortions of human motivation. The desire for chastity must precede the bond of marriage and continue to grow by the grace of God into the perfection of love and purity. Indeed, the desire for chastity and its pursuit should only lead spouses to embrace married love and each other with still greater affection. Through it one comes to recognize and experience one's spouse as helpmate. Couples must strive then not to see the sacrament of matrimony as given to them as making the passions licit and so a means of defrauding themselves of the salvation offered them in Christ. The law commands that marriage be pursued as a great good. Yet, grace encourages us to an everlasting and incorrupt purity and chastity in every state of life.
Whoever, then, mounts to this summit of gospel perfection is, by reason of his great virtuousness, raised far above the whole of the law. Despising everything that Moses commanded as insignificant, he knows that he is solely under the grace of the Savior, by whose help he realizes that he has arrived at this most sublime condition. Sin, then, has no dominion over him, `because the love of God that has been poured out in our hearts by the Holy Spirit, who has been given to us,' excludes every disposition of any other kind. Nor can he desire forbidden things or disdain things that are commanded, since all his concentration and all his longing are constantly fixed upon the divine love, and to such a degree does he not take delight in base things that he does not even make use of those things that have been conceded him. In the law, however, in which the rights of spouses are observed, it is impossible for the stings of carnal desire not to flourish, even though a roving lasciviousness is restrained and given over to only one woman. It is difficult for the fire, to which fuel is purposely added, to stay within defined limits such that it does not break free and set ablaze whatever it touches. Even if there is always something to block it, so that it is not permitted to flare up outside, it still burns while restrained, because the will itself is guilty and its familiarity with sexual intercourse quickly carries it away to the excesses of adultery. But those whom the grace of the Savior has inflamed with a holy love of incorruption burn up all the thorns of carnal desires with the fire of the Lord's love, such that a dying ember of vice does not diminish the coolness of their integrity.