The story of Onan in Genesis 38 troubles many. Why would God strike down a man for what seems like a private sexual decision? The punishment appears harsh, even disproportionate. But when we examine the passage through the lens of Reformed theology, a different picture emerges—one that reveals not divine cruelty, but God’s justice protecting His covenant purposes.

 

THE STORY BEHIND THE STORY

To understand God’s judgement on Onan, we must first grasp the cultural and covenantal context. In ancient Israel, the levirate law required a man to marry his deceased brother’s widow and produce children who’d carry on the dead brother’s name and inheritance (Deuteronomy 25:5-10). This wasn’t merely a cultural custom—it was a divine ordinance designed to preserve family lines and property, and protect vulnerable widows.

When Judah’s eldest son Er died, his widow Tamar was left in a precarious position. Without children, she had no security, no inheritance, and no future. Enter Onan, Er’s younger brother, who was commanded by his father to fulfil the levirate duty. The text tells us Onan “went in to his brother’s wife, but he wasted his seed on the ground, lest he should give offspring to his brother” (Genesis 38:9).

 

THE REAL NATURE OF ONAN’S SIN

Reformed scholarship has consistently identified Onan’s primary sin not as a sexual transgression, but as covenant disobedience. Onan wasn’t simply avoiding pregnancy—he was deliberately thwarting God’s revealed will while maintaining the appearance of obedience.

Consider the calculated nature of his deception. Onan was willing to enjoy the sexual privileges of marriage with Tamar, but he refused to fulfil his covenant obligation to provide her with children and security. He took pleasure while denying responsibility. As one commentator notes, “Onan is faking his service to God, his dead brother, and Tamar, engaging in marital relations without the benefits of pregnancy or producing an heir.”

Onan’s sin was fundamentally about selfishness and covenant-breaking. He was protecting his own inheritance (since children born to Tamar would legally belong to Er’s estate) while appearing to obey his father’s command. This kind of religious hypocrisy—outward compliance masking inner rebellion—is precisely what Scripture consistently condemns.

 

WHY THE PUNISHMENT FITS THE CRIME

God’s judgement on Onan reflects several crucial theological principles:

1. The seriousness of covenant obligations. God’s commands aren’t mere suggestions—they’re binding expressions of His will. When Onan deliberately violated the levirate law, he wasn’t just breaking a cultural norm; he was rebelling against God’s revealed order for protecting the vulnerable and preserving family lines.
2. The protection of redemptive history. The genealogical line through Judah would eventually lead to King David and ultimately to Jesus Christ. Onan’s actions threatened this divine plan. While God’s purposes cannot ultimately be thwarted, His judgement on Onan demonstrates His commitment to preserving the messianic line through which salvation would come.
3. The gravity of deception before a holy God. Onan’s sin wasn’t mere weakness—it was calculated deception. He performed the motions of obedience while deliberately undermining its purpose. This kind of duplicity strikes at the heart of covenant faithfulness.

 

ADDRESSING THE “DISPROPORTIONATE” OBJECTION

Many struggle with what appears to be harsh punishment for a “private” sin. But this objection misunderstands both the nature of Onan’s transgression and the character of divine justice.

• The sin wasn’t private. Onan’s actions affected multiple parties: Tamar (denying her security and offspring), Er’s memory (refusing to preserve his name), and God’s covenant purposes (thwarting the levirate law). So, for Onan to knowingly do all this made him selfish and callous in a very high degree.
• Divine timing differs from human timing. God alone knows the full implications of every action. While Onan’s death seems sudden to us, we don’t know what additional sins he might have committed or what further damage his rebellion might have caused. Reformed theology reminds us God’s knowledge is perfect and His timing is always right.
• All sin deserves death. The Reformed understanding of human depravity teaches every sin, however “small” it appears to us, deserves divine judgement. The wonder isn’t that God judged Onan, but that He shows mercy to anyone at all. As sinners, we have no claim on continued life—every breath is an act of divine grace.

 

THE BROADER THEOLOGICAL FRAMEWORK

The Onan narrative fits into a larger biblical pattern of God’s jealous protection of His covenant purposes. Throughout Scripture, we see divine judgement falling on those who threaten or undermine God’s redemptive plan—from the flood in Noah’s day to the destruction of Jerusalem in A.D. 70.

This doesn’t make God capricious or cruel. Rather, it reveals His unwavering commitment to accomplishing salvation for His people. The same divine love that motivated the sending of His Son also motivated the judgment on Onan. Both actions serve the ultimate purpose of redemption.

 

PASTORAL APPLICATIONS

For believers wrestling with difficult passages like this, several truths emerge:

We’re to trust God’s character even when we don’t understand His actions. The God who judged Onan is the same God who gave His Son for our salvation. His justice and mercy are both perfect and harmonious.

Take covenant obligations seriously. Just as Onan’s half-hearted obedience provoked divine judgement, our own casual approach to Christian duty dishonours God and harms others.

Beware of religious hypocrisy. Going through the motions of obedience while harbouring rebellious hearts is a dangerous spiritual condition that Scripture consistently condemns.

 

THE GOSPEL CONNECTION

Ultimately, the story of Onan points us to our need for a perfect covenant keeper. Where Onan failed in his obligations, Christ succeeded perfectly. He fulfilled every requirement of God’s law, even unto death. The judgement that fell on Onan for covenant disobedience fell on Christ for our covenant disobedience.

This gives us both sobering perspective and tremendous hope. We see in Onan’s fate what our rebellion deserves, but we also see in Christ’s sacrifice what God’s grace provides. The same divine justice that struck down Onan was satisfied by Christ’s atoning work on our behalf.

 

CONCLUSION: TRUSTING DIVINE WISDOM

The question “Why did God kill Onan?” finds its answer not in human notions of proportionality, but in divine wisdom and covenant faithfulness. Onan’s judgement wasn’t arbitrary—it was the righteous response to deliberate covenant breaking that threatened God’s redemptive purposes.

As Christians, we’re called to trust that God’s ways are higher than our ways, His thoughts higher than our thoughts. The same God who judged Onan with perfect justice also loved the world enough to send His Son. In both actions, we see the perfect harmony of divine attributes working together for the ultimate good of God’s people and the glory of His name.

 

WHY DID GOD KILL ONAN? RELATED FAQs

Did Onan practice contraception, and does this passage condemn birth control? Scholars largely reject interpreting the passage as a condemnation of contraception. John Calvin emphasised Onan’s sin was his defrauding of his brother’s memory and his deception, not the method he used. The passage addresses covenant obligations within the specific context of levirate marriage, not general principles about family planning. Most theologians argue applying this text to modern contraception discussions represents a serious misreading of the passage’s intent.

• Why didn’t God also judge Judah, who refused to give Tamar to his third son Shelah? Reformed commentators note Judah’s failure was different in nature—he acted from fear and procrastination rather than Onan’s calculated deception. Derek Kidner suggests Judah’s sin was more passive neglect, while Onan’s was active covenant-breaking disguised as obedience. Additionally, Judah later repented when confronted by Tamar’s pregnancy, showing a heart capable of conviction. God’s timing in judgement often reflects not just the gravity of sin but the condition of the heart and potential for repentance.
• How does this passage relate to the Catholic doctrine of mortal vs. venial sin? Reformed theology rejects the Catholic distinction between mortal and venial sins, teaching instead that all sin deserves death but Christ’s atonement covers all sin for believers. From a Reformed perspective, Onan’s immediate judgement doesn’t indicate his sin was worse than others, but rather demonstrates that God has the sovereign right to execute judgement at any time. The passage illustrates divine prerogative in timing rather than degrees of sin severity.

Was Onan’s punishment unique, or are there other similar judgements in Scripture? Scholars point to several parallel divine judgements for covenant violations: Nadab and Abihu’s strange fire (Leviticus 10), Uzzah touching the ark (2 Samuel 6), and Ananias and Sapphira’s deception (Acts 5). Bruce Waltke notes these judgements typically involve deliberate violations of clear divine commands, often with an element of deception or presumption. The pattern suggests God’s particular concern for maintaining the integrity of His covenant relationships and prescribed worship.

• Could Onan have been saved if he had lived longer and repented? Reformed theology affirms God’s elect cannot ultimately perish, while the reprobate cannot truly repent unto salvation. Since we don’t know Onan’s eternal destiny, Reformed scholars like Gordon Wenham suggest we should focus on the covenant implications rather than speculating about his salvation. The passage serves as a warning about the seriousness of covenant obligations rather than a definitive statement about anyone’s eternal fate.
• How do we view the apparent silence about this practice in other biblical cultures? Commentators acknowledge the Hebrew Bible doesn’t explicitly condemn similar practices outside the levirate context. This strengthens the interpretation that Onan’s judgment was specifically about covenant disobedience. Calvin argued the silence elsewhere proves the sin wasn’t the sexual act itself but the violation of sacred duty. This contextual approach allows Reformed theology to maintain consistency while avoiding legalistic applications to unrelated situations.

What does this passage teach about God’s involvement in human reproduction and family planning? Scholars emphasise God’s sovereignty over conception and birth while distinguishing between descriptive and prescriptive elements in the narrative. Matthew Henry noted the passage demonstrates God’s care for preserving family lines essential to His redemptive purposes rather than establishing universal rules about reproduction. Reformed theologians see this as an example of God’s particular providence in salvation history rather than a general template for understanding divine involvement in all human fertility decisions.

 

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