Roman Catechism 22.20

Chapter 22 — Part II: The Sacraments — Matrimony

Section 20. Twofold Consideration of Marriage — When these matters have been explained, it should be taught that matrimony is to be considered from two points of view, either as a natural union, since it was not invented by man but instituted by nature; or as a Sacrament, the efficacy of which transcends the order of nature.