Elder Jeffery R. Holland answered these very questions in General Conference. He explained precisely why it is absolutely vital we remain morally clean.
We declare that one who uses the God-given body of another without divine sanction abuses the very soul of that individual. . . . In exploiting the body of another — which means exploiting his or her soul — one desecrates the Atonement of Christ, which saved that soul and which makes possible the gift of eternal life. And when one mocks the Son of Righteousness, one steps into a realm of heat hotter and holier than the noonday sun. You cannot do so and not be burned.
In case that isn’t convincing enough, read on:
Please, never say: “Who does it hurt? Why not a little freedom? I can transgress now and repent later.” Please don’t be so foolish and so cruel. You cannot with impunity “crucify Christ afresh.” “Flee fornication,” Paul cries, and flee “anything like unto it,” the Doctrine and Covenants adds. Why? Well, for one reason because of the incalculable suffering in both body and spirit endured by the Savior of the world so that we could flee. We owe Him something for that. Indeed, we owe Him everything for that. “Ye are not your own,” Paul says. “Ye [have been] bought with a price: therefore glorify God in your body, and in your spirit, which are God’s.” In sexual transgression the soul is at stake—the body and the spirit ( Ensign , Nov. 1998, 76).
According to Elder Holland, our bodies are gifts that should not be tarnished by immoral activities. The Savior purchased them with his blood in the Garden of Gethsemane ; we owe it to Him to keep them clean. And, as Elder Holland pointed out, immorality damages the soul—both our bodies and our spirits.
Another reason why you should live the law of chastity is that it will prepare you to have a stronger, happier marriage in the future. Think of the mistrust that could develop in a marriage if one of the partners had been immoral earlier in life. You strengthen your future marriage by living the law of chastity today. A modern prophet has promised us this. President Benson taught, “When we… keep ourselves morally clean, we will experience the blessings of increased love and peace, greater trust and respect for our marital partners, deeper commitment to each other, and therefore a deep and significant sense of joy and happiness” (President Benson, New Era , Jan. 1988, 5–6).
A third reason why it’s so important we must obey the law of chastity is because immorality leads to hate, not love. President Benson taught this as well by saying:
Do not be misled by Satan’s lies…There is no joy to be found in breaking the law of chastity. Just the opposite is true. There may be momentary pleasure. For a time it may seem like everything is wonderful. But quickly the relationship will sour. Guilt and shame set in. We become fearful that our sins will be discovered. We must sneak and hide, lie and cheat. Love begins to die. Bitterness, jealousy, anger, and even hate begin to grow. All of these are the natural results of sin and transgression ( New Era , Jan. 1988, 5–6).
As you can see, there are many reasons why it’s vital we live the law of chastity.
–go to http://ldswhy.com, select “stuff from the book” and watch the video about implosion…