A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
lev 20:2GIVING ONE'S SEED TO MOLECH. (Lev. 20:1-27)
Whosoever . . . giveth any of his seed unto Molech--(See on Lev 18:21).
the people of the land shall stone him with stones, &c.--Criminals who were condemned to be stoned were led, with their hands bound, without the gates to a small eminence, where was a large stone placed at the bottom. When they had approached within ten cubits of the spot, they were exhorted to confess, that, by faith and repentance, their souls might be saved. When led forward to within four cubits, they were stripped almost naked, and received some stupefying draught, during which the witnesses prepared, by laying aside their outer garments, to carry into execution the capital sentence which the law bound them to do. The criminal, being placed on the edge of the precipice, was then pushed backwards, so that he fell down the perpendicular height on the stone lying below: if not killed by the fall, the second witness dashed a large stone down upon his breast, and then the "people of the land," who were by-standers, rushed forward, and with stones completed the work of death (Mat 21:44; Act 7:58).
lev 20:4If the people of the land do any ways hide their eyes from the man, &c.--that is, connive at their countrymen practising the horrid rites of Molech. Awful was it that any Hebrew parents could so violate their national covenant, and no wonder that God denounced the severest penalties against them and their families.
lev 20:7Sanctify yourselves therefore, and be ye holy--The minute specification of the incestuous and unnatural crimes here enumerated shows their sad prevalence amongst the idolatrous nations around, and the extreme proneness of the Israelites to follow the customs of their neighbors. It is to be understood, that, whenever mention is made that the offender was "to be put to death" without describing the mode, stoning is meant. The only instance of another form of capital punishment occurs in Lev 20:14, that of being burnt with fire; and yet it is probable that even here death was first inflicted by stoning, and the body of the criminal afterwards consumed by fire (Jos 7:15).
lev 20:20they shall die childless--Either by the judgment of God they shall have no children, or their spurious offspring shall be denied by human authority the ordinary privileges of children in Israel.
lev 20:24I . . . have separated you from other people--Their selection from the rest of the nations was for the all-important end of preserving the knowledge and worship of the true God amid the universal apostasy; and as the distinction of meats was one great means of completing that separation, the law about making a difference between clean and unclean beasts is here repeated with emphatic solemnity.