William Burkitt on 1 Corinthians 6:18

Flee fornication.

Note, 1. The apostle's advice to escape fornication; and that is, to flee it, namely, by shunning all occasions of it, all temptations leading to it, all incentives and provocations of it, not suffering our eye to wander, or our thoughts to muse, much less to dwell, upon any unlawful or ensnaring object.

Flee fornication.

Note, 2. The argument our apostle uses to flee fornication; because other sins are without the body.

Quest. But how is the apostle to be understood when he says, all other sins are without the body?

Ans. Thus, though all other outward sins, as drunkenness, murder, theft, &c. have the body as an instrument for committing them; yet in this sin of uncleanness the body is not only the instrument, but the object also, for the unclean person doth not only sin with his body, but he sins against his body.

Uncleanness leaves that blot and brand of ignominy and baseness upon the body which no other sin doth: degrading it from that excellent honour whereunto God advanced it in its natural condition, by making it the member of an harlot.