What is the meaning of “sins against his body” in 1 Corinthians 6:18?
First Corinthians 6:18 is toward the end of the section on sexual morality. He says that the body is not meant for sexual morality but should be dedicated to the Lord (1 Corinthians 6:13b). We cannot serve both our sinful sexual desires and the Lord. We can only have one master.
He reminds us that the body is raised with the spirit (1 Corinthians 6:14). And then he explains that our bodies belong to Christ (1 Corinthians 6:15). God has high standards for our bodies. He expects us not to unite them with evil purposes (1 Corinthians 6:15b-16).
With the same principle given to us in Genesis about marriage, the uniting of two people to become one flesh, Paul applies this principle to our relationship with Jesus (1 Corinthians 6:17). He commands the Corinthians, and us, to flee sexual immorality (1 Corinthians 6:18).
Then follows the explanation that every sin we commit we commit outside the body. If we still something, we do it with our hands. But it doesn’t affect the body. Sexual sin is the only sin that the body is directly involved in. And the sin that we commit sexually violates our own bodies (1 Corinthians 6:18b).
The reason why this is such a bad thing for us and our bodies is that they belong to God and the Holy Spirit dwells in us. They become the temples of the Holy Spirit (1 Corinthians 6:19). God gives us the Holy Spirit at salvation (Ephesians 1:13-14). The very presence of God dwells within Christians. Jesus paid for every Christian, including our bodies, on the cross (1 Corinthians 6:20).
We glorify God with our bodies because the Holy Spirit dwells in us and Jesus paid for our freedom from all addictions and sins, including sexual sin. Our bodies belong to Jesus. This is why we must flee sexual morality and all of its temptations to glorify God with every member of our bodies.