Leviticus 18:4

4.Ye shall therefore keep my statutes and my judgments. Because it is no less difficult to correct vices, to which men have been long accustomed, than to cure diseases of long standing, especially because people in general so pertinaciously cleave to bad examples, God adduces His statutes, in order to recall the people from the errors of their evil habits into the right way. For nothing is more absurd than for us to fix our minds on the actions of men, 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. With this object He commands His Law to be regarded not once only, as we have already seen, lest the Israelites should abandon themselves to filthy lusts; but He diligently inculcates upon 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 heathen nations, between whom and His people He had interposed, as it were, a wall of partition.