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. Though some of the incests here forbidden were practised by some particular persons among the heathen, yet they were disallowed and detested, unless among those nations who had become barbarous, and were quite given up to vile affections. Observe,

I.That which is forbidden as to the relations here specified is approaching to them to uncover their nakedness, Lev 18:6.

1.It is chiefly intended to forbid the marrying of any of these relations. Marriage is a divine institution; this and the sabbath, the eldest of all, of equal standing with man upon the earth: it is intended for the comfort of human life, and the decent and honourable propagation of the human race, such as became the dignity of man's nature above that of the beasts. It is honourable in all, and these laws are for the support of the honour of it. It was requisite that a divine ordinance should be subject to divine rules and restraints, especially because it concerns a thing wherein the corrupt nature of man is as apt as in any thing to be wilful and impetuous in its desires, and impatient of check. Yet these prohibitions, besides their being enacted by an incontestable authority, are in themselves highly reasonable and equitable. (1.) By marriage two were to become one flesh, therefore those that before were in a sense one flesh by nature could not, without the greatest absurdity, become one flesh by institution; for the institution was designed to unite those who before were not united. (2.) Marriage puts an equality between husband and wife. "Is she not thy companion taken out of thy side?" Therefore, if those who before were superior and inferior should intermarry (which is the case in most of the instances here laid down), the order of nature would be taken away by a positive institution, which must by no means be allowed. The inequality between master and servant, noble and ignoble, is founded in consent and custom, and there is no harm done if that be taken away by the equality of marriage; but the inequality between parents and children, uncles and nieces, aunts and nephews, either by blood or marriage, is founded in nature, and is therefore perpetual, and cannot without confusion be taken away by the equality of marriage, the institution of which, though ancient, is subsequent to the order of nature. (3.) No relations that are equals are forbidden, except brothers and sisters, by the whole blood or half blood, or by marriage; and in this there is not the same natural absurdity as in the former, for Adam's sons must of necessity have married their own sisters; but it was requisite that it should be made by a positive law unlawful and detestable, for the preventing of sinful familiarities between those that in the days of their youth are supposed to live in a house together, and yet cannot intermarry without defeating one of the intentions of marriage, which is the enlargement of friendship and interest. If every man married his own sister (as they would be apt to do from generation to generation if it were lawful), each family would be a world to itself, and it would be forgotten that we are members one of another. It is certain that this has always been looked upon by the more sober heathen as a most infamous and abominable thing; and those who had not this law yet were herein a law to themselves. The making use of the ordinance of marriage for the patronizing of incestuous mixtures is so far from justifying them, or extenuating their guilt, that it adds the guilt of profaning an ordinance of God, and prostituting that to the vilest of purposes which was instituted for the noblest ends. But,

2.Uncleanness, committed with any of these relations out of marriage, is likewise, without doubt, forbidden here, and no less intended than the former: as also all lascivious carriage, wanton dalliance, and every thing that has the appearance of this evil. Relations must love one another, and are to have free and familiar converse with each other, but it must be with all purity; and the less it is suspected of evil by others the more care ought the persons themselves to take that Satan do not get advantage against them, for he is a very subtle enemy, and seeks all occasions against us.

II.The relations forbidden are most of them plainly described; and it is generally laid down as a rule that what relations of a man's own he is bound up from marrying the same relations of his wife he is likewise forbidden to marry, for they two are one. That law which forbids marrying a brother's wife (Lev 18:16) had an exception peculiar to the Jewish state, that, if a man died without issue, his brother or next of kin should marry the widow, and raise up seed to the deceased (Deu 25:5), for reasons which held good only in that commonwealth; and therefore now that those reasons have ceased the exception ceases, and the law is in force, that a man must in no case marry his brother's widow. That article (Lev 18:18) which forbids a man to take a wife to her sister supposes a connivance at polygamy, as some other laws then did (Exo 21:10; Deu 21:15), but forbids a man's marrying two sisters, as Jacob did, because between those who had before been equal there would be apt to arise greater jealousies and animosities than between wives that were not so nearly related. If the sister of the wife be taken for the concubine, or secondary wife, nothing can be more vexing in her life, or as long as she lives.

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, Deu 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, Deu 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 Mat 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.

None of you shall approach to any that is near of kin to him--Very great laxity prevailed amongst the Egyptians in their sentiments and practice about the conjugal relation, as they not only openly sanctioned marriages between brothers and sisters, but even between parents and children. Such incestuous alliances Moses wisely prohibited, and his laws form the basis upon which the marriage regulations of this and other Christian nations are chiefly founded. This verse contains a general summary of all the particular prohibitions; and the forbidden intercourse is pointed out by the phrase, "to approach to." In the specified prohibitions that follow, all of which are included in this general summary, the prohibited familiarity is indicated by the phrases, to "uncover the nakedness" [Lev 18:12-17], to "take" [Lev 18:17-18], and to "lie with" [Lev 18:22-23]. The phrase in this sixth verse, therefore, has the same identical meaning with each of the other three, and the marriages in reference to which it is used are those of consanguinity or too close affinity, amounting to incestuous connections.