Chapter 22 — Part II: The Sacraments — Matrimony
Section 39. Unity Of Marriage — Though some of the ancient Patriarchs are not to be blamed for having married several wives, since they did not act thus without divine dispensation, yet Christ our Lord has clearly shown that polygamy is not in keeping with the nature of Matrimony. These are His words: For this cause shall a man leave father and mother, and shall cleave unto his wife, and they shall be two in one flesh; and He adds: wherefore they are no more two but one flesh. In these words He makes it clear that God instituted marriage to be the union of two, and only two persons. The same truth He has taught very distinctly in another passage, wherein He says: Whosoever shall put away his wife and marry another, committeth adultery against her; and if the wife shall put away her husband, and be married to another, she committeth adultery. For if it were lawful for a man to have several wives, there is no reason why he who takes to himself a second wife, along with the wife he already has, should be regarded as more guilty of adultery than if he had dismissed his first wife and taken a second.