In Leviticus, the people are gathered at Sinai to receive the law. Chapter 18 deals with various sexual relationships and is bookended with God’s call for His people to set themselves apart from the practices of Egypt, which they had just left, and from those of Canaan, the place Yahweh was bringing them to.
The list of prohibitions is divided into three sections, moving from blood relations, to blood relations that are combined with marriage, to sexual relations in which no flesh relation is involved. The first two sections are done not in the common language of “knowing” or “lying with,” but are expressed as “uncovering nakedness.” This recalls the shame and fear in the garden when the man and woman saw that they were naked and hid themselves from God. They tried to cover themselves with fig leaves, but God covered them through the sacrifice of animals. The word “approach” is also used 3 times. The Hebrew is the same word which is elsewhere translated “offering,” again linking sexual relationships with approaching the altar with sacrifices.
John Calvin summed up the chapter. “Since I am the eternal God, and separated from all others which the Gentiles foolishly make to themselves, and since I have chosen you to myself as my peculiar people, I would have you, as you ought to be, pure and separated from all defilements.”
“This is not just about behavior, but also about what is established as expected norm. Israel is to ‘guard’ the judgments and statutes of Yahweh. Israel is not only to do what Yahweh requires, but to protect and defend Yahweh’s words as the norms, as the expected walk and life of Israelites. Guarding ‘statutes and ordinances’ is particularly important in situations, like our own, where biblical sexual norms are ignored or attacked. Our responsibility is not only to pursue sexual purity, but to defend publicly God’s public norms of sexual behavior.” (Leithart)
This is where Paul picks up in 1 Corinthians 5. He rebukes the church at Corinth for harboring and allowing a man guilty of sexual immorality to continue in his sin and in their fellowship. They are not helping him by being silent, but are actually putting the whole church in danger. This sin spreads like leaven. It may not cause everyone else to become ensnared in the same thing, but it rips apart the integrity of the body. As Paul says in the next chapter, “Do you not know that your bodies are members of Christ? Shall I then take the members of Christ and make them members of a prostitute? Never! Or do you not know that he who is joined to a prostitute becomes one body with her?” and again pointing to Genesis, “For, as it is written, ‘The two will become one flesh.'” We must be fierce enemies of our own sin, and be bold enemies of each other’s.