Maintaining good physical health is a stewardship responsibility that comes with our calling. We owe this obligation to our Creator God just as surely as we have spiritual responsibilities toward Him. We may deem these physical responsibilities as less important, but that does not nullify them.
Paul uses "body" in a dual sense, as both the spiritual body—the church—and the physical body of each member. Sin works to destroy both, and God did not create us to sin.
The sin here is fornication, porneia, which includes a broad range of sexual sins that pervert the right, godly use of sex. Paul uses it to illustrate sin's destructiveness. Sin is somewhat like junk food: It may "taste" good to the senses for a while, but before it is through, it will come back and harm us with its destructive properties. Junk food may taste good going down, but all the while, it is depriving the body of life-giving nutrients it needs to be truly strong.
In Genesis 1:28, God gave mankind dominion and responsibility to rule over His creation. Our own lives and bodies are the closest and most specific areas of God's creation over which we are to rule. In Genesis 2:15, God commands us to dress and keep His creation, giving us more specific direction in this obligation. To dress and keep means we are to beautify, enhance, embellish, and improve the raw product, along with maintaining it and inhibiting its decay and degeneration. In Genesis 4:7, God admonishes Cain—and us in principle—that a desire to go contrary to God's desires will always be part of this mix. Sin lies at the door, He warns, but we must master it. In essence, we must stir up the spirit in us to discipline ourselves. In combining these major principles, we can see that God means our major areas of operation in His purpose are those closest to us.
John W. Ritenbaugh
Eating: How Good It Is! (Part Five)