Commentary - Leviticus 18:6-18

Bird's-eye view

In this section of Leviticus, the Lord lays down foundational laws concerning sexual purity, specifically prohibiting incestuous relationships. This is not an arbitrary list of taboos. Rather, it is the architectural blueprint for the covenant family, the basic building block of a holy nation. God is defining the proper boundaries and relationships within the household, which is a microcosm of the nation and the church. The surrounding nations, particularly Egypt and Canaan, were characterized by sexual chaos, and their practices had defiled the land itself. God is setting His people apart by teaching them the grammar of godly order. The phrase "uncover nakedness" is a euphemism for sexual relations, and the repeated prohibitions establish a sacred space within the family, protecting its integrity, authority structures, and peace. These laws are rooted in creation order and are therefore not merely ceremonial regulations that pass away, but are abiding moral principles that define what is holy, just, and good for all time.

The logic of the prohibitions flows from the principle of "one flesh." A man and his wife are one flesh, and therefore, her near relations become his near relations, and vice versa. This is about honoring the created lines of authority and affection. To violate these boundaries is to introduce confusion, rivalry, and a profound dishonoring of the very persons God has placed in authority over you or in a position of protected trust. This is God, the great Father, teaching His children how to build a healthy home, which is the nursery of both culture and covenant.

Outline

Context In Leviticus

Leviticus 18 is a central chapter in what is often called the "Holiness Code" (Leviticus 17-26). Having established the sacrificial system for dealing with sin and uncleanness, God now turns to the practical, daily conduct required of a people who dwell in His presence. The chapter begins with a stark warning: "You shall not do as they do in the land of Egypt, where you lived, and you shall not do as they do in the land of Canaan, to which I am bringing you" (Lev 18:3). This sets up a fundamental antithesis. The sexual ethics of Israel are to be a direct repudiation of the pagan world. The laws that follow are not suggestions for a better lifestyle; they are the boundary markers between the covenant community and the world, between life and death. The chapter concludes by warning that the land itself vomits out inhabitants who practice such defilements. Therefore, these laws are tied to Israel's tenure in the Promised Land and, by extension, to the stability and fruitfulness of any society that would seek God's blessing.

Key Issues

The Grammar of God's House

Every house has rules. These rules are not arbitrary; they reflect the character and priorities of the head of the house. When God establishes His house, the nation of Israel, He gives them His house rules. The laws in Leviticus 18 are the grammar of a godly household. They teach us how relationships are supposed to be structured. The world, then and now, promotes a sexual Esperanto, a universal language of chaotic desire where every verb conjugates with "I want." But God gives His people a holy language, with a firm grammar that distinguishes between subject and object, between parent and child, between brother and sister.

The central concept is "nakedness," which in Scripture represents not just physicality but also honor and vulnerability. To "uncover nakedness" is to violate a person's honor in the most intimate way. The prohibitions are designed to protect the vulnerable and to uphold the lines of authority that God has woven into the fabric of creation. A father's authority is honored by not violating his wife. A mother's dignity is protected. The unique, non-sexual bond between siblings is preserved. These are not just rules about who can have sex with whom. They are rules about how to build a civilization that honors God, starting in the living room.

Verse by Verse Commentary

6 ‘None of you shall approach any blood relative of his to uncover nakedness; I am Yahweh.

This is the foundational, governing principle for the entire section. The Hebrew is literally "a man, a man shall not approach the flesh of his flesh." This establishes the sphere of prohibition: one's own kin, the family circle. The purpose is "to uncover nakedness," a standard biblical euphemism for sexual intercourse. And the reason for this law is grounded in the very nature of the Lawgiver: "I am Yahweh." This is not a suggestion from a sociologist. This is a command from the Creator who designed the family and knows how it is meant to function. His identity is the basis of our obedience. He is the Lord, and therefore He has the absolute right to define the moral structure of reality.

7 You shall not uncover the nakedness of your father, that is, the nakedness of your mother. She is your mother; you are not to uncover her nakedness.

The first specific prohibition concerns one's mother. But notice the phrasing. It begins with the father's nakedness. A man's wife is his own "flesh," and so to have relations with his mother is to violate his father. This is a profound statement about the one-flesh union of marriage. A man's wife is so identified with him that a violation of her is a direct assault on his honor. The command is then stated plainly: "She is your mother." That relationship defines the boundary. The reason is not biological risk, though that is a real consequence; the reason is theological. The mother-son relationship is a sacred, non-sexual bond of nurture and respect. To sexualize it is to defile one of God's foundational structures for human society.

8 You shall not uncover the nakedness of your father’s wife; it is your father’s nakedness.

This extends the principle to a stepmother. Even if she is not your biological mother, she has entered into a one-flesh union with your father. Therefore, her nakedness is your father's nakedness. This is precisely the sin that Paul condemned with such vehemence in Corinth (1 Cor. 5:1). It is a direct usurpation of the father's authority and position. In the ancient world, taking a man's wife or concubine was tantamount to claiming his throne, as we see with Absalom and his father David's concubines. This law protects the integrity of the patriarchal line of authority within the family.

9 The nakedness of your sister, either your father’s daughter or your mother’s daughter, whether born at home or born outside, their nakedness you shall not uncover.

This covers sisters and half-sisters, regardless of the circumstances of their birth ("born at home or born outside"). The sibling relationship is to be a non-sexual one of camaraderie and mutual protection. To introduce sexual relations here is to twist and corrupt a fundamental bond. Brothers are to be protectors of their sisters' purity, not predators. This law establishes the family as a safe place, a sanctuary from the sexual chaos of the world.

10 The nakedness of your son’s daughter or your daughter’s daughter, their nakedness you shall not uncover; for their nakedness is yours.

The prohibition extends to granddaughters. The reason given is striking: "for their nakedness is yours." This means that a man's descendants are a continuation of his own flesh, his own line. To violate a granddaughter is a form of self-defilement, a grotesque violation of the natural order of generations. The grandfather's role is one of patriarchal blessing and protection, not exploitation. This law protects the generational structure of the family.

11 The nakedness of your father’s wife’s daughter, born to your father, she is your sister; you shall not uncover her nakedness.

This verse seems to reiterate the prohibition against a half-sister on the father's side, emphasizing that because she is "born to your father," she is your sister and the prohibition stands. It closes any potential loophole someone might try to create regarding step-siblings. If you share a father, the boundary is absolute. The law is concerned with the covenantal and social reality of the family, not just bare biology.

12 You shall not uncover the nakedness of your father’s sister; she is your father’s blood relative.

Now the prohibitions move to aunts. A relationship with a paternal aunt is forbidden because she is the "blood relative" of your father. Again, the principle is one of solidarity. To violate her is to violate your father's house and his own flesh and blood. It is an act of disrespect to the entire preceding generation.

13 You shall not uncover the nakedness of your mother’s sister, for she is your mother’s blood relative.

The same logic applies to a maternal aunt. She is your mother's near kin. The lines of family relationship create zones of non-sexual intimacy. An aunt should be a figure of respect and affection, and this law protects that relationship from being corrupted by sexual sin.

14 You shall not uncover the nakedness of your father’s brother; you shall not approach his wife; she is your aunt.

Here the prohibition is stated in a slightly different way. It begins by forbidding the violation of a paternal uncle, and then clarifies that this means not approaching his wife. This reinforces the one-flesh principle. The uncle and his wife are one unit. To have relations with your aunt by marriage is to commit a sin against your uncle. She is identified by her relationship to him: "she is your aunt."

15 You shall not uncover the nakedness of your daughter-in-law; she is your son’s wife; you shall not uncover her nakedness.

This protects the bond between a man and his son. The daughter-in-law has become one flesh with the son. For the father to have relations with her would be a catastrophic betrayal of his son, destroying the generational trust within the family. It would be to steal from his own child in the most profound way imaginable.

16 You shall not uncover the nakedness of your brother’s wife; it is your brother’s nakedness.

This is the law that John the Baptist cited when he confronted Herod Antipas for taking his brother Philip's wife, Herodias. A man's sister-in-law is off-limits because her nakedness "is your brother's nakedness." This law had one specific, God-ordained exception: the Levirate law (Deut. 25:5-6), where a man was commanded to marry his deceased brother's childless widow in order to raise up an heir for his brother. But that was a specific provision to protect the family line, not a general permission. Apart from that duty, the boundary stood firm.

17 You shall not uncover the nakedness of a woman and of her daughter, nor shall you take her son’s daughter or her daughter’s daughter, to uncover her nakedness; they are blood relatives. It is lewdness.

This law prohibits marrying a woman and then also marrying her daughter or granddaughter. It prevents the confounding of generations. A man cannot be a husband to one woman and a son-in-law to her at the same time. He cannot be a husband to a woman and a grandfather-in-law to her. Such relationships create an impossible and tangled web of obligations and roles. God calls it lewdness, a word that signifies a wicked and deliberate plan of depravity. It is a confusion of the created order.

18 And you shall not marry a woman in addition to her sister as a rival while she is alive, to uncover her nakedness.

This verse has been the subject of much debate. It prohibits marrying a woman's sister "as a rival" while the first wife is still living. This was the situation with Jacob, Leah, and Rachel, and the rivalry it created was a source of immense strife. Some have argued this verse implicitly permits polygamy as long as you don't marry sisters. Others argue it is a specific prohibition against a particular kind of polygamous union that was known to be especially destructive. What is clear is that it identifies rivalry as the key problem. God's design from the beginning was one man and one woman, and every deviation from that pattern, while sometimes accommodated in the Old Testament, always brought with it a harvest of sorrow, jealousy, and strife.

Application

It is tempting for modern Christians to look at a list like this and dismiss it as an ancient purity code for a different time. But that would be a grave mistake. These laws are rooted in the created order. They define the nature of family, and the family is God's first institution. A society that blurs these lines is a society that is coming apart at the seams. Our culture's rampant sexual confusion, its celebration of deviancy, and its assault on the family are not signs of progress but of decay. We are becoming like the Canaanites, and we should not be surprised if the land begins to vomit us out as well.

For the Christian, these laws should drive us to gratitude. They show us that God cares about the details of our lives. He wants our families to be places of peace, honor, and safety, not chaos and exploitation. They also should drive us to the cross. Who among us has perfectly kept the spirit of this law, which is a law of perfect love and honor for our kin? Our hearts are full of disordered desires. Our family histories are often tangled with sin. We are all guilty of uncovering nakedness in some way, whether in thought, word, or deed. Our only hope is in the one who came to cover our nakedness and shame with His own righteousness. Jesus is the true protector of the family, and it is only by being washed in His blood and walking in His Spirit that we can begin to build households that reflect the beautiful and holy order of our Father's house.