Marriage between a man and a woman is not only a human idea. It comes from the natural order.
a man will leave his father and mother and be united to his wife: Marriage involves shifting loyalty from parents to a spouse.
they will become one flesh: Marriage and its commitments make it the most basic covenant among people. Marriage is a powerful image of Israel’s covenant with God (Hosea 2:14–23) and of Christ’s relationship to the Church (Ephesians 5:22–32). God designed marriage to be a permanent, exclusive relationship between a man and a woman. The family it creates is the foundation of human society.