Today we examine the sin of Onan and whether God directly killed Onan merely for the sin of contraception or for something more?

Before I begin this article, know from the outset that I uphold the teaching of the Catholic Church with regard to sexual morality and contraception. And while I believe and practice the Catholic teaching, I will suggest that the sin of Onan in Genesis 38:9 is not chiefly about the sin of contraception (by way of coitus interruptus) but rather relates to Messianic sacrilege.

First off, what is Onanism?

Webster’s Dictionary defines Onanism as:

1:masturbation
2:coitus interruptus
3:self-gratification

Onanism in the Context of Levirate Marriage:

Onanism is named after the biblical Onan who in Genesis 33 is told by his father, the Patriarch Judah (father of one of the twelve tribes of Israel), to have sex his dead brother’s widow Tamar so that she is not childless. Having sex with the widow of your brother is called “Levirate marriage.”

It is called “Levirate” marriage because the the Latin word “levir” means “husband’s brother.” Centuries after the time of Judah and Onan, Levirate marriage was mandated by God through Moses in Deuteronomy 25:5-6.

If brothers dwell together, and one of them dies and has no son, the wife of the dead shall not be married outside the family to a stranger; her husband’s brother shall go in to her, and take her as his wife, and perform the duty of a husband’s brother to her. And the first son whom she bears shall succeed to the name of his brother who is dead, that his name may not be blotted out of Israel.

Levirate marriage is interesting because it a biblically sanctioned form of either fornication/adultery. For example, Judah’s son Er dies and leave his wife Tamar a widow. His younger brother Onan is required to have sex with Er’s widow Tamar and give her children. This happens whether Onan is not married (sex with Tamar would normally be fornication) or whether Onan is already married to another woman (sex with Tamar would then normally be adultery). It’s not clear from the text, but if the union of the man and the widow constitutes a real marriage, then he’d have multiple wives (sex with Tamar would require polygamy).

Either way, Onan and Tamar are having sex outside of natural law of marriage between one man and one woman, and the arrangement is sanctioned by God. (It’s a situation requiring a footnote.) Moreover, the child produced by these sexual relations would NOT belong to Onan’s house or lineage, but rather to his dead brother Er as Deuteronomy later makes apparent.

The Death of Onan after “Spilling Seed” in Genesis 38:

Here is the precise situation of Er (the deceased), Tamar (Er’s widow), and Onan (younger surviving brother of Er) in Genesis 38:

Then Judah said to [his son] Onan, “Go in to your brother’s wife [Tamar], 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 when he went in to his brother’s wife he spilled the semen on the ground, lest he should give offspring to his brother. And what he did was displeasing in the sight of the Lord, and he slew him also.

Onan’s sin by spilling his semen on the ground is so great that God immediately kills him. This sin of Onanism is terribly grave.

Catholic Apologists (including myself in two my own books) have pointed to Onanism in Genesis 38 as a prohibition against contraception. And they are right to do so, but God did not kill Onan merely for spilling his semen outside of Tamar. Thousands of men have spilled their seed through masturbation and coitus interruptus before, during, and after this time period, and none of them, as far as we know, received a direct death penalty from the Lord.

Why then did God kill Onan in this special case?

Might I suggest that Onan’s sin was especially grave because he was the eldest surviving son of the patriarch Judah. As such he is designated ancestor for the line of the Messiah of Israel. Our Lord Jesus Christ is the Lion of Judah and Matthew and Luke’s Gospels show that Christ descends from the genetic tribe of Judah.

The narrative goes on to show that this widow Tamar grows desperate so that she veils herself as a prostitute and hired herself out to Judah who does not know that the prostitute is actually his daughter in law. And from their illicit union springs the Messianic line descending into Jesus Christ Himself. Tamar is one of the few women explictly named in the geneology of Christ in Matthew:

and Judah the father of Perez and Zerah by Tamar, and Perez the father of Hezron, and Hezron the father of Ram. (Gen 1:3)

Jewish Irony of Sexual Rights

From a Jewish point of view, the story is ironic. Onan has the right to have sex with Tamar and he spills his seed and despises his birthright as a Messianic forebear. Judah their father actually pays to have sex with Tamar, and he plants the seed and by doing so skips over his sons. The sons no longer have the privilege of being in the lineage of Jesus Christ. This is why, I believe, Onan is killed directly by God. Onan was not likely the first man to masturbate or practice coitus interruptus (both are sins). His GREATER sin was that he despised the Messianic dynasty of the Christ.

Onan engages in coitus interruptus and the Lord slew him. Judah the father engages in prostitution, adultery, and incest…and he lives. The deciding factor over life and death here is willingness to produce a genetic line in accord with the promises of God.

A Final Thought on Judah as Messianic Forebear:

Genesis repeatedly flips the divine inheritance rights of the first born son. Abraham bears Ishmael first and later Isaac. But Isaac is given the covenantal Messianic birthright. Isaac bears Esau and Jacob. But Jacob the younger wins the covenantal Messianic birthright by way of trickery.

Jacob’s first four sons (in order) are: Reuben, Simeon, Levi, and Judah. But the first three lose their birthrights:

• In Genesis 34, the second and third born Simeon and Levi lose their status with their father Jacob for their violence.
• In Genesis 35, Reuben the first born copulates with his step-mother and loses the rights as first-born of Israel.
• In Genesis 36, we read of the descendents of Esau – those that did not receive the covenantal birthright.
• In Genesis 37, Judah intervenes to have Joseph sold as a slave, rather than be killed or left in a waterless pit. This shows Judah as righteous and rightly next in line for the covenantal blessing.
• In Genesis 38, we have the story of Er, Onan, and Tamar with Judah copulating with his daughter-in-law Tamar.

It’s obvious that the narrative from Gen 34-38 is trying to establish not 1-Reuben, 2-Simeon, or 3-Levi as the rightful heir of Abraham, but the fourth born Judah as the rightful heir. Judah’s sons are so sinful that God arranges (by trickery of Tamar) for Judah to copulate with Tamar and skip over his sons altogether.

Conclusion: Sexual Ethics and the Messiah

It’s stunning for any reader of the Bible to see how casually it mentions prostitution, fornication (eg. Samson), adultery, and polygamy. Abraham even seems willing (twice) to share his beautiful wife sexually with rulers so as not to be killed himself.

It almost seems that God totally tolerates sexual sins among the great male saints of the Old Testament. That is is why it is so surprising when God directly intervenes and kills Onan for his sexual sin. This is why I think we can conclude that the “sin of Onan” was not merely contraception by way of coitus interruptus. Rather, Onan’s sin was he was interfering with the dynasty of the promised “Seed of Adam and Abraham” – Our Lord Jesus Christ.

The theological purpose of the book Genesis is track “the Seed” from Adam > Abraham > Isaac > Jacob > Judah. And it seems that Gen 34-38 is all a transition to highlight Judah. If so, then the sin of Onan is made profoundly grave not because its mere contraception, but that it’s contraceiving the plan of God for Judah’s messianic dynasty leading to “the Promised Seed” of Genesis 3:15, who is the Messiah.

If you’d like to learn more Old Testament history, check out my book on Judaism and Catholicism: The Crucified Rabbi and sign up for online biblical, historical, and theological classes at the New Saint Thomas Institute.