What does Genesis 38:8 mean?
After his wicked son Er has been killed by the Lord (Genesis 38:6–7), Judah turns to his second son Onan. He tells Onan to take Er's widow Tamar as his wife. Onan's specific duty is to care for Tamar as a wife, with special emphasis on providing her with children, so his departed brother would have some offspring by proxy.While the practice seems strange today, it was a strong custom in the region at the time. The tradition was intended to keep a man's family line from being "cut off," if possible. It also served the interests of the widow, who would be left destitute and helpless without children to support her later in life. This "levirate marriage" would also become the standard practice of Israel (Deuteronomy 25:5–6), though the Law would later allow for a man to opt out of taking his brother's widow as a wife in this way.