Commentary - Leviticus 20:17-21

Bird's-eye view

In this section of the Holiness Code, the Lord continues to lay out the boundaries for covenant life among His people. These are not arbitrary regulations designed to make life difficult; they are architectural drawings for a sane and sacred society. God is holy, and He has chosen to dwell in the midst of Israel. Therefore, Israel must be holy. This holiness is not an abstract concept; it manifests in concrete practices, particularly in the realm of family and sexual ethics. The prohibitions here against various forms of incest and ritual impurity are about protecting the integrity of the family, which is the basic building block of society. These laws define and defend the created order against the chaotic and destructive impulses of fallen human desire. The penalties prescribed, being "cut off" or dying "childless," underscore the gravity of these offenses. Such sins do not merely harm the individuals involved; they defile the land and threaten the covenant community's relationship with their holy God.

The central logic is this: God has established certain creational boundaries. The family is a sacred institution with a defined structure. To violate that structure through incestuous relationships is to commit a kind of social blasphemy, a rebellion against the way God made the world. Likewise, the laws regarding menstrual purity are not about hygiene in the first instance, but are a part of the Bible's symbolic worldview, teaching Israel about the profound realities of life and death, clean and unclean. To disregard these distinctions is to trample on God's pedagogy. Ultimately, these laws point forward to Christ, who alone perfectly honored all of God's boundaries and who cleanses His people from all defilement, making them truly holy so they might dwell with God forever.

Outline

Context In Leviticus

Leviticus 20 is the counterpart to Leviticus 18. In chapter 18, God laid out the prohibited sexual relationships. Here in chapter 20, He attaches the specific penalties for those violations. This chapter is a core part of what scholars call the "Holiness Code" (Leviticus 17-26), a section of the law that repeatedly emphasizes the theme, "You shall be holy, for I the LORD your God am holy." The immediate context is God's instruction to Israel after bringing them out of Egypt and before bringing them into Canaan. He is setting them apart from the corrupt practices of both the nation they left and the nations they are about to dispossess. These laws are therefore definitional for Israel's identity as a people. They are not just for personal morality but for national survival. The land itself is personified as vomiting out inhabitants who defile it with such practices (Lev. 18:28). This chapter functions as the judicial enforcement section of God's holy constitution for His people.

Key Issues

The Architecture of a Holy People

When God builds a nation, He starts with the family. When God builds a holy nation, He gives laws to protect the holiness of the family. The modern world sees sexual prohibitions as restrictive and arbitrary, a list of "thou shalt nots" that inhibit personal freedom and expression. But this is to fundamentally misunderstand what law is for. God's law is not a cage; it is a blueprint. It is the architectural design for a flourishing society. Just as a builder must respect the laws of physics and engineering to erect a sound structure, a society must respect God's moral and creational laws to build a culture that is sound, stable, and blessed.

The laws in this passage are all about boundaries. They define the proper channels for sexual expression, which is to be within the covenant of marriage between one man and one woman who are not close relatives. Incestuous relationships blur and destroy the distinct roles God has designed for family members: a sister is to be a sister, not a wife; an aunt is to be an aunt, not a lover. To violate these boundaries is to introduce chaos and confusion into the most basic unit of society. It is an assault on the created order. The penalties are severe because the threat is existential. A people who will not govern their loins will not long govern their land. They will be spewed out, because they have made themselves vile in the sight of the holy God who dwells among them.

Verse by Verse Commentary

17 ‘If there is a man who takes his sister, his father’s daughter, or his mother’s daughter, so that he sees her nakedness and she sees his nakedness, it is a disgrace; and they shall be cut off in the sight of the sons of their people. He has uncovered his sister’s nakedness; he bears his guilt.

The prohibition is against marrying or having sexual relations with a half-sister, whether from one's father or mother. The phrase "sees her nakedness" is a standard biblical euphemism for sexual intercourse. This act is not described as a simple mistake or a minor infraction; it is a chesed, a word that here means a disgrace, a shameful and wicked thing. The penalty is that they shall be "cut off." This means excommunication, expulsion from the covenant community. They are to be put out of the camp in full public view, "in the sight of the sons of their people," so that the judgment is seen and the lesson is learned. This is a corporate issue. The sin defiles the community, and the community must purge the evil from its midst. The final clause, "he bears his guilt," reinforces personal responsibility. There is no excuse. He has violated a fundamental creational boundary, and the consequences are his to bear.

18 If there is a man who lies with a menstruous woman and uncovers her nakedness, he has laid bare her flow, and she has uncovered the flow of her blood; thus both of them shall be cut off from among their people.

This law deals not with incest, but with ritual purity. Under the ceremonial law, a woman was considered unclean during her menstrual period, as was anything she touched (Lev. 15:19-24). This was not because menstruation is sinful, but because in the symbolic world of the Old Testament, any flow of blood from the body represented a loss of life, a brush with death. Since God is the living God, approaching Him required ceremonial cleanness, a symbolic separation from death and decay. For a man to have relations with his wife during this time was to treat this sacred distinction with contempt. He "laid bare her flow," intentionally ignoring the sign of uncleanness. Both parties are culpable, and both are to be "cut off from among their people." This demonstrates how seriously God took His symbolic pedagogy. These were audio-visual aids to teach Israel about life and death, holiness and sin. To ignore the lesson was to fail the course, and the result was expulsion from the school of God.

19 You shall also not uncover the nakedness of your mother’s sister or of your father’s sister, for such a one has made naked his blood relative; they will bear their guilt.

The prohibition now extends to one's aunt. An aunt is a "blood relative," and the bond of kinship must be honored and protected, not violated by sexual desire. To "uncover the nakedness" of an aunt is to throw the family structure into confusion. It is a man treating his mother's or father's generation as his own, erasing the lines of authority and respect that are essential for a stable family. The phrase "they will bear their guilt" indicates that both the man and his aunt are responsible for this sin. While the death penalty is not explicitly mentioned here as it is for other offenses, the guilt remains before God, and the consequences, both social and divine, will surely follow.

20 If there is a man who lies with his aunt, he has uncovered his uncle’s nakedness; they will bear their sin. They will die childless.

This verse clarifies the previous one, focusing specifically on the wife of a father's brother, one's paternal aunt by marriage. The offense is described as uncovering "his uncle's nakedness." This is a key principle in biblical sexual ethics: a husband and wife are one flesh. Therefore, to have relations with a man's wife is to commit a deep offense against the man himself. It is a violation of the uncle's honor and his marital bond. The penalty specified here is unique: "They will die childless." This is a divine curse. In a culture where children were seen as the primary blessing of God and the means of carrying on one's name and inheritance, this was a devastating judgment. God Himself would intervene to ensure that this illicit union would be fruitless, a dead end. Their sin against the family line would be punished by the termination of their own line.

21 If there is a man who takes his brother’s wife, it is an impure act; he has uncovered his brother’s nakedness. They will be childless.

This prohibition must be understood in its context. This is not referring to the Levirate law, where a man was commanded to marry his deceased brother's childless widow to raise up an heir for him (Deut. 25:5-6). This law applies to a situation where the brother is still alive, or where he has left children. To take a brother's wife under these circumstances is an act of adultery or a profound violation of the family bond. It is an niddah, an impure thing, a menstrual-like uncleanness. The logic is the same as with the uncle: he has uncovered his brother's nakedness, violating the one-flesh union. And the penalty is the same as for sleeping with an uncle's wife: "They will be childless." God promises to enforce this law by closing the womb. This sin is an attack on the integrity and continuity of a brother's house, and so God judges it by making the sinner's own house a cul-de-sac.

Application

The modern reader, steeped in a culture of sexual autonomy, is likely to find these laws archaic and strange. But the principles they embody are timeless. God created us, and He knows how we are to live. Our sexuality is not a recreational playground but a sacred stewardship. It is designed to be expressed within the beautiful and strong boundaries of covenantal marriage.

First, we learn that the family is God's institution, and He sets the rules. The blurring of familial roles through incestuous behavior is as destructive today as it was in ancient Israel. Our society's confusion on this front is a sign of deep decay. The church must be a place where the creational goodness of distinct family roles, father, mother, son, daughter, uncle, aunt, is taught and cherished.

Second, we learn that God cares about what we do with our bodies. The ceremonial laws about bodily discharges are fulfilled in Christ, who makes us clean once and for all. We no longer observe ritual uncleanness. But the underlying principle remains: our bodies are temples of the Holy Spirit, and we are to honor God with them (1 Cor. 6:19-20). We are not to be governed by our base impulses, but by the Word of God. The world says, "If it feels good, do it." The Bible says, "Be holy, for I am holy."

Finally, we see the gravity of sin. These sins result in being cut off from the community and in divine curses like childlessness. This reminds us that all sin, ultimately, separates us from the life-giving presence of God. The wages of sin is death. But the good news of the gospel is that Jesus came to bear our guilt and our curse. On the cross, He was "cut off" from His people, exiled from the presence of the Father, so that we who trust in Him might be brought near. He bore the curse of our lawlessness so that we might receive the blessing of fruitfulness, becoming children of God and heirs of eternal life. The laws of Leviticus show us the disease in all its ugliness; the gospel of Christ provides the only cure.