If a person is sexually active before marriage, he has a mental attachment to past partners that takes away the uniqueness of sex with his lifelong mate. This is like the story about the young man who found a locket he liked at a jewelry store and gave it to his girlfriend. They later broke up, but he still liked that locket so much he began buying one to give to each successive girlfriend. When he finally found the girl he would marry, he went to look for a present for her. Sure enough, he got her the same locket. She was thrilled when she opened the box, but even though he liked the locket, it was no longer special. He had given the same gift to a lot of girls.
(contributed by Josh McDowell)