Chapter 19 [XVII.]—Blessing of Matrimony.
In matrimony, however, let these nuptial blessings be the objects of our love—offspring, fidelity, the sacramental bond. 2131 Offspring, not that it be born only, but born again; for it is born to punishment unless it be born again to life. Fidelity, not such as even unbelievers observe one towards the other, in their ardent love of the flesh. For what husband, however impious himself, likes an adulterous wife? Or what wife, however impious she be, likes an adulterous husband? This is indeed a natural good in marriage, though a carnal one. But a member of Christ ought to be afraid of adultery, not on account of himself, but of his spouse; and ought to hope to receive from Christ the reward of that fidelity which he shows to his spouse. The sacramental bond, again, which is lost neither by divorce nor by adultery, should be guarded by husband and wife with concord and chastity. For it alone is that which even an unfruitful marriage retains by the law of piety, now that all that hope of fruitfulness is lost for the purpose of which the couple married. Let these nuptial blessings be praised in marriage by him who wishes to extol the nuptial institution. Carnal concupiscence, however, must not be ascribed to marriage: it is only to be tolerated in marriage. It is not a good which comes out of the essence of marriage, but an evil which is the accident of original sin.
See above, ch. 11, and On Original Sin, ch. 39.