Lust is powerful and addictive. Look at the huge pornography industry. But Christ said, “I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart” (Matthew 5:28).
Yet, the Bible rejoices in sex and sexual desire. Genesis 1 depicts God creating sex through male and female. He called His creations very good. In Genesis 2:23, before God, naked Adam characterized naked Eve as bone of his bone and flesh of his flesh. The Song of Solomon celebrates sexual love, for example with one admiring the other’s body when the other was going in for sex (Song of Solomon 5, 7).
Sex should unify two persons, not just physically, but emotionally, mentally, and spiritually.
But sex without marriage means the parties only want to be united physically, with each holding onto their own life. They are splitting their bodies from their souls.
Sex should be an integrated act. It should re-confirm each party belonging completely and exclusively to the other. Thus, sex should be limited to marriage.
Lust is different from sexual desire. When a man lusts for a woman, he wants her body only, but not any other parts of her. He has dehumanized her.
Lust is also an excessive desire. One can be totally driven by lust, making it the center of one’s life. It is like an idol. After getting the other’s body, one still feels empty. There is no deep fulfillment in lust.
The passage on lust (Matthew 5:27-30) also points to eyes and hands. Eyes refer to what one perceives, and hands refer to actions. Have the right perception. Know that physical attraction is good but is just skin deep and can’t be meaningful. Also take the right action. Run away from lustful environments.
Sex in marriage is wonderful, but it cannot replace God as the center of our life.
Christ constantly refers Himself as the bridegroom, who accepts and loves us, His bride. Through faith, we become absolutely beautiful in Christ’s eyes. Christ becomes the center of our life. Only He could give meaning to our life, with deep fulfillment.
Summarized from a Time Keller sermon:
情欲也是一种过度性的欲望。一个人可能完全被它控制, 使情欲成为这个人生活的中心。情欲像一个偶像， 即使得到对方的身体，仍然会感到空虚，无法给予人深深的满足。