Leviticus 18 sharply describes Egyptian and Canaanite practices as defiling abominations for which the land vomits out its inhabitants. They appear particularly corrupt, including marrying a sister, two sisters, or an aunt.
Yet these familiar patriarchal practices are not presented as wrong. Abraham married his sister (Genesis 20:12); Jacob married the sisters Leah and Rachel; even Moses resulted from a later-forbidden union, Amram marrying his aunt Jochebed (Exodus 6:20). How can the Torah call such acts abominations when Israel’s greatest ancestors did not avoid them?
First we must determine whether all prohibitions belong to one group and are all termed abominations. The chapter’s structure says otherwise. This distinction explains Abraham and Amram; Jacob requires separate discussion.
The key is distinguishing kinship prohibitions, arising from relatedness between man and woman, from other sexual prohibitions.
Closed paragraph breaks divide three main units; the last divides by content into prohibitions and conclusion, producing four parts:
- Introduction: a double warning against Egyptian and Canaanite customs and a command to observe the LORD’s laws (verses 1–5).
- Kinship prohibitions: relatives with whom relations are forbidden (verses 6–16).
- Additional prohibitions: a woman and her daughter, two sisters, male homosexual intercourse, and bestiality (verses 17–23).
- Conclusion and warning: against defiling acts of the land’s nations (verses 24–30).
Kinship prohibitions begin “None of you shall approach to any that is near of kin to him, to uncover their nakedness” (verse 6). The woman is forbidden through her relationship to the man. A woman and daughter or two sisters in the additional group, however, are forbidden because of the relationship between the women and combining them, rather than either being the man’s kin.
Evaluative terms such as “wickedness,” “profanation,” “abomination,” and “perversion” appear only in the additional group, absent from kinship prohibitions.
Kinship rules include apparently universal, longstanding prohibitions, such as relations with one’s mother, alongside extensions given only to Israel after Sinai’s covenant. Uncritical accounts of Abraham and Sarah and Amram and Jochebed support paternal half-sisters and aunts belonging to these extensions.
The introduction anticipates both groups. Condemnation of Egyptian and Canaanite practices (verse 3) prepares for additional prohibitions later attributed to the nations. Observing the LORD’s statutes and ordinances (verses 4–5) prepares for kinship rules, including new covenant laws.
The conclusion’s impurity and abominations may concern the immediately preceding additional prohibitions rather than the earlier kinship unit, since that group expressly uses “wickedness,” “abomination,” and “perversion.”
This explains Abraham and Sarah and Amram and Jochebed: their unions were permitted before the Torah and only later added to forbidden kinship. It does not yet explain Jacob’s two sisters, in the additional group containing sharp condemnations. Why is he not criticized if such prohibitions concern abominations?
Though in that group, the two-sisters rule has no term like “abomination” or “perversion.” It apparently presents a moral problem rather than sexual abomination: “And thou shalt not take a woman to her sister, to be a rival to her” (verse 18). It prevents normally loving sisters becoming rival wives (see Brown–Driver–Briggs, entry tz-r-r).
Jacob initially sought Rachel alone. Laban’s deception left Leah already his wife. The Torah depicts him facing an imposed situation rather than initiating marriage to sisters. Requiring him to surrender Rachel, for whom he worked and whom he intended to marry, was unreasonable; marrying her alongside Leah was the lesser evil. This explains the absence of criticism.
Nevertheless, his story illustrates the prohibition’s rationale. The marriage made the sisters rivals, producing jealousy and struggle. Its painful consequences show precisely the moral problem the rule warns against.
