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? For, as it is written, “The two will become one flesh.” But he who is joined to the Lord becomes one spirit with him. Flee from sexual immorality. Every other sin a person commits is outside the body, but the sexually immoral person sins against his own body. Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, for you were bought with a price. So glorify God in your body. 

1 Corinthians 6: 15-20

Run like the wind! When referring to sexual immorality, a better phrase would be run from it. 

Why do you think Paul says that sexual immorality sins against the person’s own body?  Doesn’t addiction to substances or gluttony also sin against the body? 

More than a physical act, the idea of being “one flesh” indicates that there is something more. Paul indicates that there are both spiritual and physical consequences of sexual immorality. 

Practically speaking, most who read this have not been involved with a prostitute or with someone outside of marriage, but Jesus leveled the playing field with his comments in the Sermon on the Mount:

“You have heard that it was said, ‘You shall not commit adultery. But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart.” 

Matthew 5:27-28

One of the things I like best about Paul’s teaching is that he does not generally just list what we are to avoid.  So while we should “flee sexual immorality” we are reminded to recognize who we are in Christ and with that perspective, we are able to honor God with our bodies.