What is the difference between fornication and other sins?
In I Corinthians 6, Scripture states every other sin a man commits is outside the body, but fornication is unique because the one committing it sins against his own body. For the believer, sexual immorality also adulterates his union with Christ, violating fidelity to Him like marital fidelity.
Les explains from I Corinthians 6 that every sin a person commits is outside the body, but fornication is different because it is a sin against one's own body. Since the believer is now in union with Christ, he must be as careful about fidelity to Christ as husband and wife should be to each other. Paul is telling the Corinthians that their past lifestyle and taking immoral activity for granted no longer applies; as children of God they are on totally different territory and are different people. Immoral activity literally adulterates their position with Christ. If a believer commits sexual immorality, he adulterates his union with the one to whom he has been joined. Paul therefore says the believer has no business involving himself in extramarital relationships. The family and marriage relationship is holy and sanctified, ordained by God; Les illustrates this monogamy principle by noting he quit goose hunting when he learned geese are monogamous.
Flee fornication. Every sin that a man doeth is without the body; but he that committeth fornication sinneth against his own body.