John Gill Bible Commentary

The nakedness of thy father's wife shalt thou not uncover,.... That is, who is indeed a man's father's wife, but not his own mother, but a stepmother or mother-in-law; or otherwise this law would coincide with the former; a man lying with such an one is accursed by the law, Deu 27:23; such an incestuous copulation was that of Reuben with Bilhah, and Absalom with his father's concubines or secondary wives, and such an incestuous marriage was that of the Corinthians, Co1 5:1; and of Antiochus Soter, king of Syria, with Stratonice his mother-in-law (c): and even it was criminal to do this after a father's death, as Jarchi interprets it; and though she was only betrothed, and not married, and the father dead after such betrothing; as Gersom; nay, though she was divorced by the father, yet was not lawful for the son to have, no, not after his death: it is thy father's nakedness; being espoused to him, and so one flesh with him; and the son and father being one flesh, such a mixture must be unlawful; and since then the nakedness of a mother-in-law is the father's, then surely that of an own mother's must be so likewise, which confirms a sense given of it in Lev 18:7, Cicero (d) exclaims against such marriages as incredible and unheard of, as instances of unbridled lust and singular impudence. (c) Vid. Julian. in Misopogon, p. 72, &c. (d) Orat. 14. pro A. Cluentio Avito.