Question: "Why were a husband and wife considered unclean after they had sexual relations?"
Answer: Leviticus 15:18 says, “When a man has sexual relations with a woman and there is an emission of semen, both of them must bathe with water, and they will be unclean till evening.” This command must be speaking of sexual intercourse between a married couple, since the Law elsewhere forbids adultery and fornication. So, any time a husband and wife had sexual intercourse, they would be considered unclean for the rest of the day. It seems strange, if marital sex is not sinful, that it would make a married couple unclean.
Being unclean according to the Law was not synonymous with being sinful. The Old Testament Law speaks of two kinds of uncleanness—moral and ceremonial. Moral uncleanness was caused by immoral acts such as those listed in Leviticus 20:10–21, with punishments ranging from childlessness to death. The “impurity” caused by marital sex was of the ceremonial kind and carried no punishment.
An unclean person had to avoid touching holy things and follow the Law’s instructions to return to a state of cleanness. Uncleanness kept a person from approaching the sanctuary (Numbers 5:3). An unclean person could not eat consecrated food or even bring it as a tithe (Leviticus 7:20–21; Deuteronomy 26:14 ). If a person was unclean during the time of Passover, he or she had to wait one month before celebrating the feast (Numbers 9:6–13 ).
In addition to marital sexual relations, there were other causes of ceremonial uncleanness. A nocturnal emission of semen caused a man to be ceremonially unclean that day, and he had to spend the day outside the camp (Deuteronomy 23:10–11). Also, women were ceremonially unclean when menstruating (Leviticus15:19–23) and after giving birth (Leviticus 12:1–8). In marriage, two become one (Genesis 2:24; Matthew 19:4–6) and share the ceremonial uncleanness in sexual union (Leviticus 15:18). But there is nothing sinful or immoral about marital sex, which was God’s invention and decree for humans, even before sin entered the human race (Genesis 1:28).
We can assume any number of reasons God had for making these rules governing uncleanness, from physical hygiene for individuals and communities to helping couples appreciate the specialness of His gift of sex. In contrast, some ancient societies had descended into a shockingly foul and savage state, living more like wild animals driven by every kind of impulse rather than living as God’s highest creation, made in His image (Genesis 1:26–27).
But the ultimate purpose for everything in the Law is spiritual. In the case of the laws governing uncleanness, the purpose was to show the people of Israel that God is holy and mankind is not. The fact that normal sexual relations caused a married couple to become ceremonially unclean shows that we are impure before God, even when we are not committing outright sin. We are fallen people living in a fallen world, and even the day-to-day activities of life make us unclean. We require cleansing before we can approach the Holy God.
God told Israel, “You are to be holy to me because I, the Lord, am holy, and I have set you apart from the nations to be my own” (Leviticus 20:26). Israel’s lack of holiness was kept front-and-center in the Law. “What is the use of the Law? It was given . . . to show that we sin” (Galatians 3:19, CEV). What Israel needed—and what all of us need—is the faith of Abraham, because “those who have faith are children of Abraham” (verse 7), that is, those who trust God’s promises are recipients of God’s blessing.