28 And if you defile the land, it will vomit you out as it vomited out the nations that were before you.
22 " 'Keep all my decrees and laws and follow them, so that the land where I am bringing you to live may not vomit you out.
(Read Leviticus 20:10-27)
These verses repeat what had been said before, but it was needful there should be line upon line. What praises we owe to God that he has taught the evil of sin, and the sure way of deliverance from it! May we have grace to adorn the doctrine of God our Saviour in all things; may we have no fellowship with unfruitful works of darkness, but reprove them.
Matthew Henry's Commentary on Leviticus 18:28
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.