It happened at that time that Judah went down from his brothers and turned aside to a certain Adullamite, whose name was Hirah. There Judah saw the daughter of a certain Canaanite whose name was Shua. He took her and went in to her, and she conceived and bore a son, and he called his name Er. She conceived again and bore a son, and she called his name Onan. Yet again she bore a son, and she called his name Shelah. Judah was in Chezib when she bore him.
And Judah took a wife for Er his firstborn, and her name was Tamar. But Er, Judah’s firstborn, was wicked in the sight of the LORD, and the LORD put him to death. Then Judah said to Onan, “Go in to your brother’s wife and perform the duty of a brother-in-law to her, and raise up offspring for your brother.” But Onan knew that the offspring would not be his. So whenever he went in to his brother’s wife he would waste the semen on the ground, so as not to give offspring to his brother. And what he did was wicked in the sight of the LORD, and he put him to death also.
Comment: You can’t hide the truth from God so you needn’t try! Maybe I’ve got it wrong but trying to flesh out this story, I think it was like this – Judah forsook his family’s custom of being ethnocentric and marrying within the wider tribal group. so he made friends with the ‘foreigner’ Hirah and was convinced to marry Shua. He rapidly had three sons. Time flies by, the marriage lasts and the oldest of their children, Er, a rotter, marries Tamar but dies before she becomes pregnant. The writer clearly indicates that God (and we don’t know how) was involved in his death.
So by local custom, of which God approved, her father-in-law ordered Er’s brother, Onan, to do his duty by his brother and to produce kids in his brother’s name. He obviously didn’t mind having sex with his sister-in-law, but kept withdrawing and ejaculating onto the ground. This didn’t please God and he joined his brother in Sheol. I don’t know how God did it but this passage definitely states that it was God’s action. This is not a ‘delicate’ story!
Prayer: Help me to realize that You are involved in every aspect of my life, O Lord.
As I read it! 