Momentarily Joseph drops out of the narrative to be replaced by his brother Judah. Judah marries a Canaanite girl by whom he has three children: Er, Onan, and Shelah. Er marries Tamar, but he is put to death by God for an unspecified sin. As a result Tamar is left a childless widow. It is then the responsibility of the next eldest son, Onan, to father a child by his sister-in-law to bear the name of the deceased. This custom is known as levirate marriage (Latin levir, “brother-in-law”), and is spelled out in detail in Deuteronomy 25:5–10. The institution is reflected in the New Testament story about the woman who was married to seven husbands (Matt. 22:23–28). In the resurrection, Jesus is asked, to whom will she belong?

Onan refuses to exercise his responsibility most li…