The Lord told Moses in simplicity, "Thou shalt not commit adultery. (Ex. 20:14)" The Lord told the Prophet Joseph Smith a similar command, when he said, "Thou shalt . . . not . . . commit adultery, nor do anything like unto it. (D&C 59:6)" Alma the Younger gave us the reason why. He taught his wayward son Corianton, "Know ye not, my son, that these things are an abomination in the sight of the Lord; yea, most abominable above all sins save it be the shedding of innocent blood or denying the Holy Ghost? (Alma 39:5)"
As we have heretofore enunciated the tenants of this doctrine as to what it is, we will now answer the question: why be morally clean?
The Case for Sexual Morality
The Lord told the ancient Israelites in the simplest of terms, "Speak unto all the congregation of the children of Israel, and say unto them, Ye shall be holy: for I the Lord your God am holy. (Lev. 19:2)"
That seems simple enough to reason with any man. David expounds slightly on why we should be holy, namely because "Thy testimonies are very sure: holiness becometh thine house, O Lord, for ever. (Ps. 93:5)" Only the Latter-day Saints understand the true purposes of the House of the Lord, and as David says, it is used to make men holy. Since no unclean thing can dwell in the presence of God, this uncleanliness the Lord speaks of must include sexual immorality; and that sexual immorality must be purged from within us.
What Rests Under the Sexual Immorality Title?
King Benjamen taught that almost everything we do could lead to sexual immorality, and that we must be ever watchful so as to not be ensnared thereby. He taught, "But this much I can tell you, that if ye do no watch yourselves, and your thoughts, and your words, and your deeds, and observe the commandments of God, and continue in the faith of what ye have heard concerning the coming of our Lord, even unto the end of your lives, ye must perish. And now, O man, remember, and perish not. (Mosiah 4:30, emphasis added)" President David O. McKay remarked, "The kind of life you live, your disposition, your very nature, will be determined by your thoughts, of which your acts are but the outward expression. Thought is the seed of action. (Treasures of Life, comp. Clare Middlemiss (1962), p. 200)"
Also included within sexual immorality is pornography. Said President Gordon B. Hinckley,
Sin it is. It is devilish. It is totally inconsistent with the spirit of the gospel, with personal testimony of the things of God, and with the life of one who has been ordained to the holy priesthood. . . . all who are involved become victims. Children are exploited, and their lives are severely damaged. The minds of youth become warped with false concepts. Continued exposure leads to addiction that is almost impossible to break. Men, so very many, find they cannot leave it alone. Their energies and their interests are consumed in their dead-end pursuit of this raw and sleazy fare. . . . It leads to fantasies that are destructive of self-respect. It leads to illicit relationships, often to disease, and to abusive criminal activity. ("A Tragic Evil Among Us", November 2004 Liahona)
I know that if we as a nation are sexually pure, faithful entirely to our spouses, and chaste in thought and deed, the Spirit of the Lord will be with us more; the nations of the earth would prosper, both temporally and spiritually; crime would diminish; and love of God and of man will increase and peace reign supreme. In the name of Jesus Christ, amen!