Neither shalt thou take a wife to her sister,.... Both of them together, as Jarchi; two sisters at one and the same time; so the Targum of Jonathan,"a woman in the life of her sister thou shall not take;''that is, in marriage, that sister being his wife; for the sense of the Targumist can never be that a man might not take a woman for his wife, she having a sister living, but not to take one sister to another, or marry his first wife's sister, whether, as Maimonides says, she was sister by father or mother's side, in marriage or in fornication:to vex [her], to uncover her nakedness; two reasons are given, why, though polygamy, or having more wives than one, was connived at, yet it was not allowed that a man should have two sisters; partly, because they would be more apt to quarrel, and be more jealous and impatient of one another, if more favour was shown or thought to be shown to one more than another; and partly, because it was a filthy and unbecoming action to uncover the nakedness of one, or lie with one so nearly related to his wife:besides her in her life [time]; from whence some have concluded, and so many of the Jewish writers , that a man might marry his wife's sister after her death, but not while she was living; but the phrase, "in her lifetime", is not to be joined to the phrase "thou shall not take a wife"; but to the phrases more near, "to vex her in her lifetime", or as long as she lived, and "to uncover her nakedness by her" , on the side of her, as long as she lived; for that a wife's sister may be married to her husband, even after her death, cannot be lawful, as appears from the general prohibition, Le 18:6; "none of you shall approach to him that is near of kin to him"; and yet it is certain that a wife's sister is near akin to a man; and from the prohibition of marriage with an uncle's wife, with the daughter of a son-in-law, or of a daughter-in-law, Le 18:14; now a wife's sister is nearer of kin than either of these; and from the confusion that must follow in case of issue by both, not only of degrees but appellation of kindred; one and the same man, who as a father of children, and the husband of their mother's sister, stands in the relation both of a father and an uncle to his own children; the woman to the children of the deceased sister stands in the relation both of a stepmother, and of a mother's sister or aunt, and to the children that were born of her, she stands in the relation both of a mother and an uncle's wife; and the two sorts of children are both brethren and own cousins by the mother's side, but of this See Gill on "Le 18:16" for more; some understand this of a prohibition of polygamy, rendering the words, "thou shall not take one wife to another"; but the former sense is best; polygamy being not expressly forbidden by the law of Moses, but supposed in it, and winked at by it; and words of relation being always used in all these laws of marriage, in a proper and not in an improper sense: there is a pretty good deal of agreement between these laws of Moses and the Roman laws; by an edict of Dioclesian and Maximian , it was made unlawful to contract matrimony with a daughter, with a niece, with a niece's daughter, with a grandmother, with a great-grandmother, with an aunt by the father's side, with an aunt by the mother's side, with a sister's daughter, and a niece from her, with a daughter-in-law to a second husband, with a mother-in-law, with a wife or husband's mother, and with a son's wife; and several of these laws are recommended by Phocylydes, an Heathen poet, at least in a poem that hears his name; and the marriage of a wife's sister after her death has been condemned by several Christian councils .
Hilchot Issure Biah, c. 2. sect. 9. Misn. Yebamot, c. 4. sect. 13. Vajikra Rabba, sect. 22. fol. 164. 1. Peaicta, Ben Gersom in loc. hyle "apud vel prope eam"; so le is sometimes used; see Nold. part.
Concord. Ebr. p. 691. Apud Mosaic. & Roman. Leg. Collat. ut supra. (tit. 6. a Pithaeo) Concil. Illiber. can. 61. Aurat. can. 17. Auxer. can.