Biblical Commentary on the Old Testament, by Carl Friedrich Keil and Franz Delitzsh, [1857-78], at sacred-texts.com
Punishments for the Vices and crimes Prohibited in Ch. 18 and 19. - The list commences with idolatry and soothsaying, which were to be followed by extermination, as a practical apostasy from Jehovah, and a manifest breach of the covenant.
Whoever, whether an Israelite or a foreigner in Israel, dedicated of his seed (children) to Moloch (see Lev 18:21), was to be put to death. The people of the land were to stone him. בּאבן רגם, lapide obruere, is synonymous with סקל, lit., lapidem jacere: this was the usual punishment appointed in the law for cases in which death was inflicted, either as the result of a judicial sentence, or by the national community.
By this punishment the nation only carried out the will of Jehovah; for He would cut off such a man (see at Lev 17:10 and Lev 18:21) for having defiled the sanctuary of Jehovah and desecrated the name of Jehovah, not because he had brought the sacrifice to Moloch into the sanctuary of Jehovah, as Movers supposes, but in the same sense in which all the sins of Israel defiled the sanctuary in their midst (Lev 15:31; Lev 16:16).
If the people, however (the people of the land), should hide their eyes from him (on the dagesh in חעלּם and יעלּימוּ see the note on Lev 4:13-21), from an unscrupulous indifference or a secret approval of his sin, the Lord would direct His face against him and his family, and cut him off with all that went a whoring after him.
He would also do the same to every soul that turned to familiar spirits and necromantists (Lev 19:31, cf. Exo 22:17), "to go a whoring after them," i.e., to make himself guilty of idolatry by so doing, such practices being always closely connected with idolatry.
For the Israelites were to sanctify themselves, i.e., to keep themselves pure from all idolatrous abominations, to be holy because Jehovah was holy (Lev 11:44; Lev 19:2), and to keep the statutes of their God who sanctified them (Exo 31:13).
Whoever cursed father or mother was to be punished with death (Lev 19:3); "His blood would be upon him." The cursing of parents was a capital crime (see at Lev 17:4, and for the plural דּמיו Exo 22:1 and Gen 4:10), which was to return upon the doer of it, according to Gen 9:6. The same punishment was to be inflicted upon adultery (Lev 20:10, cf. Lev 18:20), carnal intercourse with a father's wife (Lev 20:11, cf. Lev 18:7-8) or with a daughter-in-law (Lev 20:12, cf. Lev 18:17), sodomy (Lev 20:13, cf. Lev 18:22), sexual intercourse with a mother and her daughter, in which case the punishment was to be heightened by the burning of the criminals when put to death (Lev 20:14, cf. Lev 18:17), lying with a beast (Lev 20:15, Lev 20:16, cf. Lev 18:23), sexual intercourse with a half-sister (Lev 20:17, cf. Lev 18:9 and Lev 18:11), and lying with a menstruous woman (Lev 20:18, cf. Lev 18:19). The punishment of death, which was to be inflicted in all these cases upon both the criminals, and also upon the beast that had been abused (Lev 20:15, Lev 20:16), was to be by stoning, according to Lev 20:2, Lev 20:27, and Deu 22:21.; and by the burning (Lev 20:14) we are not to understand death by fire, or burning alive, but, as we may clearly see from Jos 7:15 and Jos 7:25, burning the corpse after death. This was also the case in Lev 21:9 and Gen 38:24.
No civil punishment, on the other hand, to be inflicted by the magistrate or by the community generally, was ordered to follow marriage with an aunt, the sister of father or mother (Lev 20:19, cf. Lev 18:12-13), with an uncle's wife (Lev 20:20, cf. Lev 18:4), or with a sister-in-law, a brother's wife (Lev 20:21, cf. Lev 18:16). In all these cases the threat is simply held out, "they shall bear their iniquity," and (according to Lev 20:20, Lev 20:21) "die childless;" that is to say, God would reserve the punishment to Himself (see at Lev 18:14). In the list of punishments no reference is made to intercourse with a mother (Lev 18:7) or a granddaughter (Lev 18:10), as it was taken for granted that the punishment of death would be inflicted in such cases as these; just as marriage with a daughter or a full sister is passed over in the prohibitions in ch. 18.
The list of punishments concludes, like the prohibitions in Lev 18:24., with exhortations to observe the commandments and judgments of the Lord, and to avoid such abominations (on Lev 18:22 cf. Lev 18:3-5, Lev 18:26, Lev 18:28, Lev 18:30; and on Lev 18:23 cf. Lev 18:3 and Lev 18:24). The reason assigned for the exhortations is, that Jehovah was about to give them for a possession the fruitful land, whose inhabitants He had driven out because of their abominations, and that Jehovah was their God, who had separated Israel from the nations. For this reason (Lev 18:25) they were also to sever (make distinctions) between clean and unclean cattle and birds, and not make their souls (i.e., their persons) abominable through unclean animals, with which the earth swarmed, and which God had "separated to make unclean," i.e., had prohibited them from eating or touching when dead, because they defiled (see ch. 11). For (Lev 18:26) they were to be holy, because Jehovah their God was holy, who had severed them from the nations, to belong to Him, i.e., to be the nation of His possession (see Exo 19:4-6).
But because Israel was called to be the holy nation of Jehovah, every one, ether man or woman, in whom there was a heathenish spirit of soothsaying, was to be put to death, viz., stoned (cf. Lev 19:31), to prevent defilement by idolatrous abominations.