Chapter 22 — Part II: The Sacraments — Matrimony
Section 49. Fidelity — The second advantage of marriage is faith, not indeed that virtue which we receive in Baptism; but the fidelity which binds wife to husband and husband to wife in such a way that they mutually deliver to each other power over their bodies, promising at the same time never to violate the holy bond of Matrimony. This is easily inferred from the words pronounced by Adam when taking Eve as his wife, and which were afterwards confirmed by Christ our Lord in the Gospel: Wherefore a man shall leave father and mother and shall cleave to his wife and they shall be two in one flesh. It is also inferred from the words of the Apostle: The wife hath not power of her own body, but the husband: and in like manner, the husband hath not power of his own body but the wife. Justly, then, did the Lord in the Old Law ordain the most severe penalties against adulterers who violated this conjugal fidelity.