1 Corinthians 6:15

Another rhetorical question affirmed the truth. As we are members of Christ’s body, so our bodies are members of Him. This is not just clever wordplay. Our physical bodies are just as much a part of Christ-united with Him in a genuine spiritual union-as we are part of the mystical body of Christ, the church. However, Paul was not speaking here of the believer’s union with Christ by becoming a member of His mystical body, the church (1 Corinthians 12:12-26). He was metaphorically speaking of our individual union with Christ’s physical body.

When a Christian has sexual relations with a prostitute, he or she takes what belongs to God and gives it to someone else. This is stealing from God. When a Christian marries, this does not happen because God has ordained and approves of marriage (cf. 1 Corinthians 7:14). He permits us to share our bodies with our lawful mates. Taking a member of Christ and uniting it to a harlot also involves the Lord in that immoral act. Paul’s revulsion at the thought of this comes through graphically in his characteristic me genoito (lit. "May it not happen!").

"Sex outside of marriage is like a man robbing a bank: he gets something, but it is not his and he will one day pay for it. Sex within marriage can be like a person putting money into a bank: there is safety, security, and he will collect dividends. Sex within marriage can build a relationship that brings joys in the future; but sex apart from marriage has a way of weakening future relationships, as every Christian marriage counselor will tell you." [Note: Wiersbe, 1:589.]