So keep my charge never to practice any of these abominable customs that were practiced before you, and never to make yourselves unclean by them: I am the Lord your God.
Leviticus 18 is a controversial teaching to pagans. In this chapter, God lists sexual activity that is a violation of the Covenant Israel had with Him. Included in the list are incest and adultery, bestiality, and same sex relations. Pagans today also reject this teaching. But for all its Old Testament restrictive examples, the reason for the teaching is clear: God is holy and demands that holiness in marriage mark the lives of His people.
Israel lived in a culture that knew all these "abominable customs". The pagans in Egypt were sexually promiscuous in their lifestyles. The Canaanites whose land God would give to Israel practiced all the things prohibited in this list. Even in the wilderness, Israel had been tempted and had fallen into some of these sexual sins (see the accounts in the book of Numbers) because of the influence of Gentiles around them. Much pagan idolatry was accompanied by sexual activity of perverse kinds. Israel would be challenged to live by a higher, God-worshiping standard and not be their most base desires.
Application is unfortunately all too obvious today. I live in a neo-pagan culture that in the name of individuality, freedom and "human rights" promotes nearly every expression of sexuality as good in almost all "consensual" expressions. The taboos still left are incest, rape, and pedophilia. I wonder how soon these too will fall. Leviticus 18 is a foundational text for Christians to understand the powerful channel of the holiness of marital faithfulness as a great experience of human sexuality. But in a society were sexual energy is a flood of gross excess, that is increasingly fixated with pornification and casual lack of commitment, it is difficult to practice or understand these things. Yet sexual ethics for the glory of God can change everything for the Christian. I find that it moves me to reject culture and accept the corrective of God's truth!