God is such a prude! He even tells the Israelites who, or what, they can and can’t have sex with! And why would he do this? First, God establishes his authority, telling them that, “I am the Lord your God.” He has every right to command their obedience. From the very beginning God decreed that the foundation of sexual morality would be marriage. In Genesis 2 God gives the reason for marriage, a man leaving his father and mother and being united to his wife. Then there is the very clear teaching of the Ten Commandments. No less than three of the commandments speak directly to the sanctity of marriage and the family.
God’s commands are not arbitrary; they are given specifically for human flourishing. Just as God tells the Israelites that they are to honor their father and mother “so that you may live long in the land the Lord your God is giving you.” Since the Garden, Satan has filled human minds with the idea that God is a liar, that his commands are meant to keep us from flourishing, from having fun and being fulfilled. Yet every time human beings live contrary to God’s law, they suffer.
So God in his kindness and mercy tells us the proper context for sex, what we should and should not do, and sex is serious business. God uses such words in this chapter as “wickedness,” “detestable,” “defile,” and “perversion.” So the Israelites know without a doubt what the proper context for sexual relations is, and why God is telling them this. The people in Egypt and the people that surround them in Canaan practice such sexual perversity, and they must not. Here is how he puts it:
24 “‘Do not defile yourselves in any of these ways, because this is how the nations that I am going to drive out before you became defiled. 25 Even the land was defiled; so I punished it for its sin, and the land vomited out its inhabitants.
This reference to vomit is used again in God’s warning to Israel, that if they do these things he too will vomit them out of the land.
30 Keep my requirements and do not follow any of the detestable customs that were practiced before you came and do not defile yourselves with them. I am the Lord your God.’”
God bookends his commands with the same phrase; He is Israel’s ultimate authority. They are to look to him for their ethics, for what it means to live a good life, not to the surrounding cultures. As we are told in the New Testament, we are to be in the world, but not of it, so the same with Israel. Biblical sexual ethics are non-negotiable, which is especially important in our day.