What Does Genesis 38:9 Mean?

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. Onan's act is a deliberate circumvention of the levirate obligation: he uses Tamar as a wife in practice while refusing to fulfill the function for which he married her. The verse is specific about the motivation: "he knew that the offspring would not be his." His objection is not moral squeamishness; it is inheritance calculation. The son produced by the levirate union would legally be Judah's heir through Er, not through Onan. Onan would raise a child who would inherit Er's portion rather than enlarging Onan's own.

"Whenever he went in": the imperfect verb indicates repeated action, not a single incident. This is not a one-time failure of resolve but a sustained pattern of deliberate refusal. Onan went in to Tamar repeatedly; repeatedly he withdrew without completing the act. The repetition is its own verdict on his character: he had multiple opportunities to fulfill the obligation and chose, each time, to prioritize his own inheritance prospects over his brother's name and Tamar's covenantal standing. The frequency makes clearer that this was not weakness but willful policy.

The covenantal severity of Onan's act lies in its targeting: he is not simply avoiding an undesired marriage but exploiting Tamar's dependent position while refusing her the one thing the law required the marriage to provide. She cannot remarry freely while bound to the levirate structure; she must wait for Onan's compliance; she has no recourse against his refusal. He has effectively trapped her in a marriage that gives him the benefits of a wife without giving her the heir that was her right in this arrangement. The LORD's judgment in verse 10: the same swift death that took Er: reflects the gravity with which God regards this exploitation of the covenantal structure designed to protect vulnerable widows.