Leviticus 18:6 - Meaning and Application

These laws belong to the seventh commandment, and they still bind us under the gospel. They fit with the light and law of nature itself. Paul treats one case, a man having his father’s wife, as a sin so shocking that it was hardly even named among the Gentiles (1 Corinthians 5:1). Some of the incest here forbidden did happen among the heathen, but it was still judged wrong and disgusting, except among nations that had become brutal and had given themselves over to vile passions.

Notice, then, what is forbidden with these close relatives: coming near them to uncover their nakedness (Leviticus 18:6). The main point is to forbid marrying any of these relatives. Marriage is a divine institution, along with the Sabbath, the oldest of all institutions and as old as man’s life on earth. It is meant for the comfort of human life and for the proper, honorable increase of the human race, in a way that fits the dignity of human nature above the animals. Since marriage is honorable for all, these laws support that honor.

It was fitting that a divine ordinance should have divine rules and limits, especially because this is one area where corrupt human nature is especially stubborn and impulsive. These prohibitions are not only backed by unquestionable authority, they are also wise and fair. By marriage, two become one flesh. So those who were already one flesh by nature cannot sensibly become one flesh by marriage, since marriage is meant to unite people who were not already united. Marriage also puts husband and wife on one level. As Scripture says, the wife is the man’s companion, taken from his side. So if people who already stood in a natural order of superiority and inferiority were made to marry, that order would be overturned by the marriage bond, and that should not happen.

The difference between master and servant, or noble and common, rests on custom and agreement, so marriage can remove it without harm. But the difference between parents and children, uncles and nieces, or aunts and nephews, whether by blood or marriage, is built into nature itself. That kind of order lasts, and marriage cannot rightly erase it. Marriage came after nature’s order, so it cannot cancel that order. Among equals, only brothers and sisters are forbidden, whether by full blood, half blood, or by marriage. This has no such natural absurdity as the other cases, since Adam’s sons would have had to marry their sisters if the human race was to continue. Even so, God made it unlawful and detestable by positive law, to prevent sinful closeness between those who grow up together in one home and yet cannot marry without ruining one of marriage’s purposes, the widening of friendship and shared interests.

If every man married his own sister, as people would likely do from one generation to the next if it were allowed, each family would become a world of its own, and people would forget that we are members of one another. Even the more serious heathen always regarded this as shameful and abominable, and those who lacked this law still had some sense of it written on their consciences. Using the marriage ordinance to support incestuous unions does not excuse them or make them less guilty. It only adds the sin of profaning God’s ordinance and using what was made for the holiest purposes for the vilest ends.

But uncleanness with any of these relatives outside marriage is also surely forbidden here, and no less intended than marriage itself. The command also covers lustful behavior, flirtation, and anything that even looks like this evil. Relatives should love one another and enjoy free, natural conversation together, but always with purity. And the less other people suspect evil, the more careful the people themselves should be, so that Satan does not gain an advantage. He is a crafty enemy and looks for every opening against us.

Most of the forbidden relatives are named plainly. The general rule is this: if a man is forbidden to marry certain relations of his own, he is also forbidden to marry the same relations of his wife, since the two are one. The law against marrying a brother’s wife (Leviticus 18:16) had one special exception in the Jewish state. If a man died childless, his brother or nearest relative was to marry the widow and raise up offspring for the dead man (Deuteronomy 25:5). That rule fit that commonwealth alone. Now that the reason for it has ended, the exception has ended too, and the law stands in force: a man must not marry his brother’s widow.

The command in Leviticus 18:18, which forbids taking a wife along with her sister, assumes a tolerated form of polygamy, as some other laws of that time did (Exodus 21:10; Deuteronomy 21:15). But it forbids a man from marrying two sisters, as Jacob did, because jealousy and conflict would likely be greater between women who were already so closely related. If a wife’s sister is taken as a concubine, that is, a secondary wife, nothing could be more painful to the first wife, both during her life and as long as she lives.