Jamieson, Fausset and Brown on Leviticus 18:24

24. Defile not yourselves in any of these things--In the preceding verses seventeen express cases of incest are enumerated; comprehending eleven of affinity [Le 18:7-16], and six of consanguinity [Le 18:17-20], together with some criminal enormities of an aggravated and unnatural character. In such prohibitions it was necessary for the instruction of a people low in the scale of moral perception, that the enumeration should be very specific as well as minute; and then, on completing it, the divine lawgiver announces his own views of these crimes, without any exception or modification, in the remarkable terms employed in this verse.

in all these the nations are defiled which I cast out before you, &c.--Ancient history gives many appalling proofs that the enormous vices described in this chapter were very prevalent, nay, were regularly practised from religious motives in the temples of Egypt and the groves of Canaan; and it was these gigantic social disorders that occasioned the expulsion, of which the Israelites were, in the hands of a righteous and retributive Providence, the appointed instruments (Ge 15:16). The strongly figurative language of "the land itself vomiting out her inhabitants" [Le 18:25], shows the hopeless depth of their moral corruption.