{13} Flee fornication. Every sin that a man doeth is without the body; but he that committeth fornication sinneth against his own body.

(13) Another argument why fornication is to be avoided, because it defiles the body with a peculiar type of filthiness.

People's New Testament

6:18 Flee fornication. The sin must be fled. The way to avoid it is to avoid temptation. We must conquer by running away. Thus it was that Joseph prevailed.

Every sin that a man doeth is without the body. The temptations come from without and assail the man through the sense. This is the rule in the case of sin.

But he that committeth fornication sinneth against his own body. It is not said of fornication that it is not stimulated without, or that it, alone of sins, assails the body, but that it is peculiarly a sin against the body. It defiles a body which is designed to be a member of Christ, and a temple of the Holy Spirit; separates it from the union with Christ, and unites it with a harlot. The grievousness of the sin is in the desecration to such an unholy purpose of a body which has become a member of Christ, a part of the temple of God.

Wesley's Notes

6:18 Flee fornication - All unlawful commerce with women, with speed, with abhorrence, with all your might. Every sin that a man commits against his neighbour terminates upon an object out of himself, and does not so immediately pollute his body, though it does his soul. But he that committeth fornication, sinneth against his own body - Pollutes, dishonours, and degrades it to a level with brute beasts.

Jamieson-Fausset-Brown Bible Commentary

18. Flee-The only safety in such temptations is flight (Ge 39:12; Job 31:1).

Every sin-The Greek is forcible. "Every sin whatsoever that a man doeth." Every other sin; even gluttony, drunkenness, and self-murder are "without," that is, comparatively external to the body (Mr 7:18; compare Pr 6:30-32). He certainly injures, but he does not alienate the body itself; the sin is not terminated in the body; he rather sins against the perishing accidents of the body (as the "belly," and the body's present temporary organization), and against the soul than against the body in its permanent essence, designed "for the Lord." "But" the fornicator alienates that body which is the Lord's, and makes it one with a harlot's body, and so "sinneth against his own body," that is, against the verity and nature of his body; not a mere effect on the body from without, but a contradiction of the truth of the body, wrought within itself [Alford].

Matthew Henry's Concise Commentary

6:12-20 Some among the Corinthians seem to have been ready to say, All things are lawful for me. This dangerous conceit St. Paul opposes. There is a liberty wherewith Christ has made us free, in which we must stand fast. But surely a Christian would never put himself into the power of any bodily appetite. The body is for the Lord; is to be an instrument of righteousness to holiness, therefore is never to be made an instrument of sin. It is an honour to the body, that Jesus Christ was raised from the dead; and it will be an honour to our bodies, that they will be raised. The hope of a resurrection to glory, should keep Christians from dishonouring their bodies by fleshly lusts. And if the soul be united to Christ by faith, the whole man is become a member of his spiritual body. Other vices may be conquered in fight; that here cautioned against, only by flight. And vast multitudes are cut off by this vice in its various forms and consequences. Its effects fall not only directly upon the body, but often upon the mind. Our bodies have been redeemed from deserved condemnation and hopeless slavery by the atoning sacrifice of Christ. We are to be clean, as vessels fitted for our Master's use. Being united to Christ as one spirit, and bought with a price of unspeakable value, the believer should consider himself as wholly the Lord's, by the strongest ties. May we make it our business, to the latest day and hour of our lives, to glorify God with our bodies, and with our spirits which are his.