Finally, the Lord prohibits sexual relationships between those who are not related by blood, but through marriage. This includes a father’s wife (who is not the natural mother; Leviticus 18:8), an uncle’s wife (Leviticus 18:14), a daughter-in-law (Leviticus 18:15), and a sister-in-law (Leviticus 18:16). Any sexual activity is understood as the violation of the blood-kin. For example, any sexual relations with one’s sister-in-law brings shame on one’s brother.
14 You shall not uncover the nakedness of your father’s brother, that is, you shall not approach his wife; she is your aunt.