Gen 38:8-10 | TNotes | STEP | 38:8 as our law requires... . You must produce an heir for your brother: The custom that informs this episode is the law for levirate marriage (Latin levir , “husband’s brother”). By this custom, which was later incorporated into God’s law for Israel (Deut 25:5-10 ), if a man died childless, his brother or nearest relative would marry his widow to produce a child who would carry on the family name of the deceased and inherit his property. Apparently, the near kinsman had a right to refuse, but he would be disgraced in the family for refusing to perpetuate his brother’s name.

bDeut 25:5-10►

c38:9-10►

‏ Genesis 38:8-10

38:8 ^a as our law requires... . You must produce an heir for your brother: The custom that informs this episode is the law for levirate marriage (Latin levir, “husband’s brother”). By this custom, which was later incorporated into God’s law for Israel (Deut 25:5-10 ^b), if a man died childless, his brother or nearest relative would marry his widow to produce a child who would carry on the family name of the deceased and inherit his property. Apparently, the near kinsman had a right to refuse, but he would be disgraced in the family for refusing to perpetuate his brother’s name.
Summary for Gen 38:9-10: 38:9-10 ^c Onan married Tamar, but was not willing to provide an heir for his brother. He would have sex with Tamar but not fulfill his responsibility to his dead brother (38:8 ^d).