Today we need to keep emphasizing the obvious. Namely, the covenant meaning of the marriage act. It starts in Genesis; it is confirmed by the response of Jesus to the Jews of his day that marriage is for keeps. Now, that was so radical that the response of some was, “Better not to get married.” So the teaching of the Lord Jesus is that marriage itself is indissoluble, a latinized way of saying permanent, unbreakable, “for keeps.” So also with the marriage act. It ought to reflect the reality of marriage itself as made by God.
A few questions help to make this clear. Who put together in one act what we call making babies and making love? Who else but God? What the God-man taught about marriage itself also applies to the marriage act. What’s wrong with adultery, incest, prostitutes and sodomy? There are sociological reasons why they are wrong, but the bedrock reason is first and foremost they they are not marriage acts. They are essentially dishonest. They contradict the divine teaching about human love and sexuality. And that applies to marital contraception. As Pope Paul VI taught in Humanae Vitae, marital contraception is intrinsically dishonest (n.14).
John Kippley
Sex and the Marriage Covenant