Marriage was instituted by God, not invented by man (cf. Catechism of the Catholic Church, n.1603). The Creator has built it into human nature, even into the human body, in its two complementary forms, male and female. Male and female He created them (Gen.1: 27): man for woman, and woman for man, united in marriage as one flesh for the procreation of new life: Be fruitful and multiply (Gen.