Thy brother's wife - That is, if she had children. See Deuteronomy 25:5. The law here expressed was broken by Antipas in his connection with Herodias Matthew 14:3-4.

Thy brother's wife - This was an illegal marriage, unless the brother died childless. In that case it was not only lawful for her to marry her brother-in-law, but he was obliged by the law, Deuteronomy 25:5, to take her to wife.

Thou shalt not uncover the nakedness of thy brother's wife,.... Neither debauch her nor after the death of the brother marry her, that is, unless he dies without issue; and then, by another law, he was obliged to marry her, Deuteronomy 25:5; hence the Targum of Jonathan adds; by way of explanation."in the life of thy brother, or after his death, if he has children,''but then that law was but an exception from this general rule, and so did not make it void in other respects, but bound it the more strongly; and besides, it was a special and peculiar law to the Jews, until the Messiah came to make it manifest of what tribe and family he came; and the reason of it ceasing, the law itself is ceased, and so neither binding on Jews nor Gentiles: hence John the Baptist boldly told Herod to his face, that it was not lawful for him to have his brother's wife Matthew 14:3; and even such marriages were condemned by the very Heathens: Dionysius Halicarnassensis (n) relates, that Lucius Tarquinius, Superbus, his brother being removed by poison, took Tullia to wife, whom his brother Aruntus had before married; but the historian calls it , "an unholy marriage", and abominable both among Greeks and Barbarians: Plutarch also reports (o), that Marcus Crassus married the wife of his deceased brother; but such marriages are condemned by the same writer, as they are by the ancient Christians in their councils and canons (p); now by this same law, if it is not lawful for a man to have his brother's wife, then it is not lawful for her to have her sister's husband; or, in other words, if it is not lawful for a woman to marry two brothers, then it is not lawful for a man to marry two sisters: the case of Jacob will not countenance such a marriage, since he was imposed upon and deceived; and such marriages have also been disapproved of by the Heathens and Christians: Honorius the emperor married two daughters of Stilico, one after another, but the unhappy exit of both sisters showed that those marriages were not approved of by God, for they both died premature deaths, leaving no children (q):

it is thy brother's nakedness; that is, his wife is, being by marriage one flesh with him, and his brother being so to him, the relation is too near to intermarry, and more especially when there is issue by the first, which connects them strongly.

(n) Hist. l. 4. (o) In Vita M. Crassi. (p) Canon Apostol. can. 19. Concil. Neocaesar. can. 2.((q) Zonaras, l. 3. apud Zanchium de Sponsalibus, l. 4. c. 1. p. 786.

Marriage with a brother's wife was a sin against the brother's nakedness, a sexual defilement, which God would punish with barrenness. This prohibition, however, only refers to cases in which the deceased brother had left children; for if he had died childless, the brother not only might, but was required to marry his sister-in-law (Deuteronomy 25:5).

Thou shalt not uncover the nakedness of thy {h} brother's wife: it is thy brother's nakedness.

(h) Because the idolaters, among whom God's people had dwelt and would dwell, were given to these horrible incests, God charges his own to beware of them.

18:16 Thy brother's wife - God afterwards commanded, that in one case, a man should marry his brother's widow.

18:1-30 Unlawful marriages and fleshly lusts. - Here is a law against all conformity to the corrupt usages of the heathen. Also laws against incest, against brutal lusts, and barbarous idolatries; and the enforcement of these laws from the ruin of the Canaanites. God here gives moral precepts. Close and constant adherence to God's ordinances is the most effectual preservative from gross sin. The grace of God only will secure us; that grace is to be expected only in the use of the means of grace. Nor does He ever leave any to their hearts' lusts, till they have left him and his services.