How faithful should a Christian be to Christ, and what is the basic moral principle of the Bible?

Les explains that Christ is the Head of the Church, which is His Body, not its King, because believers are not subjects but joint heirs with Him. Because the believer is in union with Christ, Paul commands the same careful fidelity to Christ that a husband or wife should have toward each other. Les says this is the whole moral principle of biblical teaching. In I Corinthians 6, Paul stresses that every sin a man commits is outside the body, but fornication sins against his own body. Paul tells the Corinthians that their past immoral lifestyle is no longer their standard; as children of God they are on totally different territory and are totally different people. Immoral activity literally adulterates their position with Christ. Therefore the believer has no business involving himself in extramarital relationships, because the family and marriage relationship is holy, sanctified, and ordained by God.