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.
25. therefore I do visit the iniquity thereof upon it; and the land itself vomiteth out her inhabitants—The Canaanites, as enormous and incorrigible sinners, were to be exterminated; and this extermination was manifestly a judicial punishment inflicted by a ruler whose laws had been grossly and perseveringly outraged. But before a law can be disobeyed, it must have been previously in existence; and hence a law, prohibiting all the horrid crimes enumerated above—a law obligatory upon the Canaanites as well as other nations—was already known and in force before the Levitical law of incest was promulgated. Some general Iaw, then, prohibiting these crimes must have been published to mankind at a very early period of the world's history; and that law must either have been the moral law, originally written on the human heart, or a law on the institution of marriage revealed to Adam and known to the Canaanites and others by tradition or otherwise.