The nakedness of thy sister, the daughter of thy father, or daughter of thy mother, whether she be born at home, or born abroad, even their nakedness thou shalt not uncover.
These laws relate to the seventh commandment, and, no doubt, are obligatory on us under the gospel, for they are consonant to the very light and law of nature: one of the articles, that of a man's having his father's wife, the apostle speaks of as a sin not so much as named among the Gentiles, Co1 5:1.
Commenting on Leviticus 18:6-18
The nakedness of thy sister,.... To lie with one in so near a relation is exceeding criminal, and for which the law curses a man, Deu 27:22; and to marry her is not lawful; for though it was necessary for the propagation of mankind that a man should marry his sister, for who else could Cain and Abel marry?
The nakedness of thy sister, the daughter of thy father, or daughter of thy mother, [whether she be] born at home, or born abroad, [even] their nakedness thou shalt not uncover. (e) Either by father or mother, born in marriage or otherwise.