"...but he who commits sexual immorality sins against his own body" (1 Cor. 6:18).
Paul’s purpose in these verses is to establish two points. First, the relation between our bodies and Christ is an intimate, life-giving union. Second, sexual immorality is inconsistent with our relation in Christ and incompatible with it.
Our union with Christ is a fundamental doctrine of the Christian faith. Our bodies are the members of Christ because He purchased them with His own blood, and by His Spirit we are partakers of His life. This mystical union is compared to the union of a husband and wife, wherein the two become one. Paul’s teaching that the “believer who is joined to the Lord is one spirit with Him” does not mean that we become divine, but that the principle of life that raised Christ from the dead indwells us. “The Holy Spirit is given without measure unto Christ, and from Him is communicated to all His people who are thereby brought into common life with Him,” Hodge wrote. “This being the case, it imposes the highest conceivable obligation not to act inconsistently with this intimate and exalting relationship.”
Paul then commands the Corinthians, and thus Christians in every age, to flee sexual immorality. The reason he gives is that this sin is a crime against one’s own body. This does not mean that fornication is greater than any other sin, but it does mean that sexual immorality is a peculiar sin in its effects on the person, not so much in its physical as in its moral and spiritual effects. There is something mysterious about sexual intimacy. It is more than a physical act. It is spiritual, and thus its influences exceed the physical realm. If sex occurs outside the marriage union, it has devastating effects upon the soul, ripping apart the moral and spiritual fabric of those who engage in the sin. Because of this, and because of our union with Christ, we should flee all sexual immorality.
We should run from fornication, as Joseph did before Potiphar’s wife, because our body is a temple. This means that it is the dwelling place of God and that it is owned by Him. Under no circumstances is the temple of the Lord to be profaned. We were bought with a price, the death of Jesus Christ, and thus we are owned by Him. Therefore, we cannot act according to our sinful desires, but we must serve Christ and honor Him with our bodies.
If you are committing sexual immorality, take seriously Paul’s warnings and confess your sin to God today. If you have committed this sin in the past and confessed it to God and repented of it, be comforted that all things are made new in Christ and that He promises to heal, forgive, and remove your sins as far as he east is from the west.
