John Calvin Commentary Leviticus 18:4

"Mine ordinances shall ye do, and my statutes shall ye keep, to walk therein: I am Jehovah your God." — Leviticus 18:4 (ASV)

You shall therefore keep my statutes and my judgments. Because it is no less difficult to correct vices to which people have long been accustomed than to cure long-standing diseases, especially since people generally cling so stubbornly to bad examples, God presents His statutes to recall them from the errors of their evil habits to the right way. For nothing is more absurd than for us to fix our minds on human actions and not on God’s word, in which is to be found the rule of a holy life.

It is, therefore, just as if God would overthrow whatever had been received from long custom and abolish the universal consent of the world by the authority of His doctrine. For this purpose, He commands His Law to be regarded not once only, as we have already seen, to prevent the Israelites from abandoning themselves to filthy lusts; but He diligently teaches them that they should turn away from all abuses and keep themselves within the bounds and ordinances of His Law.

And to this refers the expression, I am the Lord your God; containing a comparison between Himself and the Gentile nations, between whom and His people He had placed, as it were, a wall of partition.