Roman Catechism 22.24

Chapter 22 — Part II: The Sacraments — Matrimony

Section 24. Although it belongs to marriage as a natural contract to be indissoluble, yet its indissolubility arises principally from its nature as a Sacrament, as it is the sacramental character that, in all its natural relations, elevates marriage to the highest perfection. In any event, dissolubility is at once opposed to the proper education of children, and to the other advantages of marriage.