Chapter 18 keeps them from dishonouring themselves in the things which belong to nature itself -- to what man ought to be in his natural relations, that he might not dishonour himself. Man ought not to do it; but, not having honoured God, he has been left to dishonour himself (compare Rom. 1). The people of God, being brought into nearness to Him, are taught on this subject. They were separated from the evil of the world they were called out of, and the reckless profligacy into which Satan had driven degraded man as his sport. Verse 6 is the great principle which is insisted on in the chapter -- not to confound the intimacies of marriage with the confidence of natural relationship. Those things are forbidden into which, in the satanic and unnatural indulgence of flesh, Satan plunged man, and to which God had given them up to work all uncleanness with greediness. The comeliness of nature is maintained; what is defiling forbidden. Jehovah's statutes and judgments were to guide them: man in probation walking in them would live.