Sexual immorality is wrong, Paul concluded, because it involves sinning against one's body, which in the case of believers belongs to the Lord through divine purchase.
6:18 In conclusion, believers should flee from fornication (porneian). Joseph is a good example to follow (Gen. 39:12). Fornication is more destructive to the sinner than other sins because the people who engage in it cannot undo their act. Gluttony and drunkenness hurt the body as well, but they involve excess in things morally neutral, and abstinence may correct their effects.
Fornication is also a specially serious sin because it involves placing the body, which is the Lord's (vv. 19-20), under the control of another illegitimate partner (cf. 7:4).156No other sin has this result. All other sins are outside or apart from the body in this sense.
"Does God then forbid the restoration of fallen leaders? No. Does He leave open the possibility? Yes. Does that possibility look promising? Yes and no. If both the life and reputation of the fallen elder can be rehabilitated, his prospects for restoration are promising. However, rehabilitating his reputation, not to mention his life, will be particularly difficult, for squandering one's reputation is a snare of the devil' (1 Tim. 3:7), and he does not yield up his prey easily."157
6:19 Another rhetorical question makes a strong important statement. Previously Paul taught his readers that the Corinthian church was a temple (naos; 3:16). The believer's body is also one. The Holy Spirit is really indwelling each of these temples (Rom. 8:9). He is a gift to us from God (cf. 1 Thess. 4:8). He is the best gift God has given us thus far. Consequently we have a moral obligation to the Giver. Moreover because He indwells us we belong to Him.
6:20 Furthermore, God has purchased (Gr. agorazo) every Christian with a great price, the blood of Jesus Christ (Rom. 3:24-25; Eph. 1:7; et al.). We belong to Him for a second reason. In view of this we should glorify God in our bodies rather than degrading Him through fornication (cf. Rom. 12:1-2). Usually the New Testament emphasis is on redemption leading to freedom from sin (e.g., Gal. 3:13; 4:5; Rev. 5:9; 14:3), but here it is on redemption leading to faithfulness to God. Even our physical bodies are to be faithful to the Lord with whom we are joined.
"The reason to glorify God in the body and not engage in sexual immorality is rooted in a new way of understanding the self."158
"What Paul seems to be doing is taking over their own theological starting point, namely that they are spiritual' because they have the Spirit, and redirecting it to include the sanctity of the body. The reality of the indwelling Spirit is now turned against them. They thought the presence of the Spirit meant a negation of the body; Paul argues the exact opposite: The presence of the Spirit in their present bodily existence is God's affirmation of the body."159
Paul's solution to the problem of the lack of discipline (chs. 5-6) was the same as his solution to the problem of divisions in the church (1:10-4:21). He led his readers back to the Cross (6:20; cf. 1:23-25).
Incest was one manifestation of carnality in the church (ch. 5), suing fellow believers in the public courts was another (6:1-11), and going to prostitutes was a third (6:12-10). Nevertheless the underlying problem was a loose view of sin, a view the unbelievers among whom the Corinthian Christians lived took. In this attitude, as in their attitude toward wisdom (1:10-4:21), their viewpoint was different from that of the Apostle Paul and God. God inspired these sections of the epistle to transform their outlook and ours on these subjects.
