Verse 17 says, "But he who is joined to the Lord is one spirit." In these three verses we can see the mystery of the union of our body with the Lord. The most crucial point in these three verses is the matter of union. Verse 17 means that since those who join their body to a prostitute become one flesh with her and become her members, the believers who are joined to the Lord in one spirit will all the more have their body become His members! This is a very crucial thought. If the mere joining of one's body with a prostitute makes two bodies one, will not those whose whole being is joined to Christ be one with Him in the body?

The apostle believes that one who is joined to the Lord is initially "one spirit" with the Lord because this is the union of spirits. But he never considered the body of a believer to be independent of his spirit. He admits that the initial joining is in the spirit, but the union of the spirit also makes the believer's body become a member of Christ. This statement is a proof of what he just said, that "the body is...for the Lord" and "the Lord [is also] for the body."

All the problems rest on the matter of union. God's children must know clearly that their own position in Christ is an uninterrupted union. Hence, our body is a member of the Lord. The life of the Lord can be manifested from our body. If the Lord were weak, anguished, and sick, we would have nothing. But since He is not, our union with Him can secure the health, power, and life of the Lord for us.

However, we must stress one point: this does not mean that since our body is a member of Christ, our body should sense all the spiritual fellowship and spiritual matters. Christians are often misled to think that since the body is a member of Christ, everything should be evidenced by the body. They think that God's presence should be felt in the body, that God shakes the body, and that the shaking of God is in the body. They think that God rules over the body directly, that the Holy Spirit fills the body, and that the Holy Spirit communicates His will to the body, using the tongue and mouth of the body to speak for Him. In this way, the body replaces the spirit in its work. As a result the spirit loses its function, and the body works for the spirit. Sometimes the body cannot endure much labor and breaks down. Furthermore, evil spirits, that is, spirits without a body, love nothing more than man's body. Their main purpose is to attach themselves to man's body. If a believer exalts the position of his body beyond what it should be, evil spirits will take the opportunity to work. This is in accordance with the law of the spiritual realm. If a believer thinks that God and His Spirit communicate with him through his body, he may expect God and His Spirit to communicate with him through his body. But God and His Spirit do not communicate directly through his body but through his spirit. If the believer still insists on pursuing after the experience of God in his body, evil spirits will take this opportunity to come into him because this is exactly what they want. The result is nothing other than evil spirits attaching themselves to the believer's body. When we speak about the union of our body with Christ, we are simply saying that the body can receive God's life and be strengthened by it, and that one should use it carefully because its position is so noble. We are not saying that the body can take over the work of the spirit.

Verse 18 says, "Flee fornication. Every sin which a man may do is outside the body, but he who commits fornication sins against his own body." The Bible considers the sin of fornication to be more serious than any other sin. This is because fornication is especially related to the body, while our body is a member of Christ. We should not be surprised that the apostle emphatically reminded and repeatedly exhorted the believers to flee fornication. We pay attention to the moral defilement of fornication. But this is not the apostle's emphasis. Other than fornication, no sin causes our body to be joined to that of another. Therefore, fornication offends the body. Other than fornication, no sin changes the members of Christ to members of a prostitute. Therefore, fornication is a sin that offends the members of Christ. Because a believer is joined to Christ, fornication becomes all the more deplorable. We can look at it another way: if fornication is so deplorable, the union of our body with Christ must be very real.