The narrative in Genesis 38 shifts away from Joseph to talk about one of his nephews: Onan.
Little is known about this character, apart from his association with certain sexual practices (known as Onanism). In fact, the Bible doesn’t really mention much about any of them, with the exception of Perez and Zerah, who is produced by the incestuous union of Judah and Tamar in Genesis 35. And even that is most likely to show the Davidic, and ultimately Messianic, lineage through Judah.
Regardless, Onan’s brief appearance is equal parts bizarre and violent. After Onan’s older brother dies as a result of being “evil in the sight of the Lord” (Genesis 38:7), Onan marries Tamar.
The instructions are explicit: Onan is to marry her in order to raise up a child for his older brother. This sets the stage for an Old Testament practice that would later referred to as Levirate marriage (Deuteronomy 25:5-6).
Except Onan isn’t a fan of the practice. He knows that the child won’t be his, and so he “spills his seed” on the ground. God is angry and takes his life also.
Two questions emerge automatically. Why did Onan not want to raise up children for his brother, and why was God so angry about that sin that He killed him for it?
Both questions can be answered with a single statement: Onan was greedy.
Any child created by Onan and Tamar would be of the lineage of Er, Onan’s older brother. This not only created someone that technically ranked higher in the family than Onan, but it also cut into the inheritance.
It could also represent lust on Onan’s part. He performed most of the duty to create a son for his brother, but not 100% of it. If he simply wanted to refuse the duty, he would’ve never slept with Tamar in the first place. As it is, he engaged in most of the act but dishonored his family by spilling his seed.
I think you can make a parallel of this story with that of Ananias and Sapphira in Acts 4. Like Onan, Ananias and Sapphira wanted to appear like they were holy, without actually making much of a sacrifice. Like Onan, they were both killed on the spot.
I don’t know if this is a lesson on greed as much as it is a lesson on trying to circumvent God’s laws while maintaining the appearance of obedience. Either way though, God knows our hearts, and since He knows our hearts, He knows what we’re really trying to do in life.
And in the case of Onan, God’s judgment on those actions was swift.
