What does Leviticus 18:30 mean?

So stick to what I've told you. Don't do any of these things that make people unclean—things that were done before you came. Don't corrupt yourselves with them. I am the Lord your God. Leviticus 18:30 - Modern Text Bible

(The passage closes with a call to loyalty and distinctiveness. God wants his people to live differently from those around them.)