Pope Francis, in his first encyclical, Lumen Fidei, tells us: “The stable union of man and woman in marriage… is born of their love, as sign and presence of God’s own love, and of the acknowledgment and acceptance of the goodness of sexual differentiation whereby spouses can become one flesh (cf. Genesis 2:24) and are enabled to give birth to a new life” (n. 52).

What makes the love between a man and woman in marriage so special, especially as opposed to same-sex unions? Marriage between a man and a woman is complementary: man loves woman (and woman, man) as different, distinct, and other. Men and women have different physical and emotional constitutions and temperaments. God’s commandment to love your neighbor as yourself, means each man (and woman) must learn to love not himself-his own physical and emotional traits-but his opposite, which isn’t always easy.