Wasn’t Onan’s sin just a sin of selfishness?
No. The book of Deuteronomy describes the punishment for refusing one’s Levirate obligation (Deut 25: 5-10). The prescribed punishment for such selfishness was only a public embarrassment, not the death penalty. In Onan’s case, there were three people violating the Law of the Levirate—-Onan, his father, and his younger brother. Only Onan, however, practiced a contraceptive behavior, and only Onan received an immediate punishment. Clearly, Onan was slain for his contraception, and the text shows how seriously God regards this sin.
Does the Bible address other sexual sins?
Yes. In alphabetical order, the Bible condemns adultery, bestiality, coitus interruptus (withdrawal), fornication, incest, masturbation, prostitution, rape, and sodomy. That eliminates everything except the honest, non-contraceptive marriage act between spouses married to each other. The Bible makes it clear that sexual intercourse is intended by God to be exclusively a marriage act.
What does the Bible say about having children?
There is no question that the Bible is pro-child. The first commandment of the Bible, “Be fruitful and multiply” (Gen 1:28) has not been cancelled. Another translation is “Be fertile and multiply.” Psalms 127 and 128 further exemplify the pro-family attitude encouraged in the Bible. Children thrive best in a family of several children where they learn to give, share, and care. (pages 7 and 13, NFPI manual)
John and Sheila Kippley
Natural Family Planning: The Complete Approach