The law of chastity is a religious law that has brought increased scrutiny, and in some cases, malevolence to the Church of Jesus Christ of Latter Day Saints. Whether this comes from the misconceptions about the practice of polygamy in church history, or more recent attention to the stance of Mormons on homosexual marriage, few people outside the church understand the context behind the LDS perspective on chastity. It does not help when those of our own membership misconstrue, misinterpret, or misunderstand the law.
For those unfamiliar with the concept, it is actually quite simple. Sexual relationships of any kind are only permissible between a husband and wife.
Polygamy is a subject for another post perhaps... and is currently a non-issue since no member can remain in good standing with the church.
In general, chastity is perhaps one of the least popular commandments. Men seem especially vulnerable to falling beneath its standard. Perhaps this is because men are biologically programmed to have tremendous desire for female companionship. Even the sight of a woman can arouse powerful feelings that impair judgement. What man has not said something that later sounded totally stupid because they were trying to make conversation with a beautiful girl? In the most serious case, remember King David, who had been hand-picked by God to rule over Israel, who bravely stood up to Goliath of Gath, and who killed tens of thousands of enemies of Israel, but when he saw Bath-Sheba bathing, he eventually fell so far as to arrange for the murder of her husband to claim her for himself...
God has bound intimacy to the commitment of marriage. Because the feelings of attraction are not similarly bound, and the intensity of these feelings can cause even good men like David to do things they would never otherwise do, and because there are so many ways to violate this law, it is perhaps the greatest difficulty of men. Compounding the frustrations of natural temptation is the prevalence of blatant disregard for the law of chastity in the form of pornography, infidelity, and homosexuality.
Even among members of the church, there are those that believe they do God a service by attacking his Apostles when they affirm the commandments prohibiting homosexual behavior and/or homosexual marriage. Whether they are well-meaning misguided individuals caught up in the fervor of rainbow-flag-waving activism, or they are just full of crap, let me affirm my belief that just as he did in Biblical times, God reveals his will and law via his Apostles. The stance of the church on homosexuality is not just a policy, or the opinion of a high-ranking member of the faith... it is the will of Jesus Christ himself.
One of the fundamental concepts behind the pro-homosexual movement is the devaluing of gender. If gender does not matter, then there are no grounds for denying marriage to couples based on gender. Apostles of Jesus Christ have declared the following on this subject: "Gender is an essential characteristic of individual premortal, mortal, and eternal identity and purpose" (The Family: A Proclamation to the World) It should not be difficult to see that gender differences are more profound than other cultural or ethnic distinctions. The "separate but equal" methods that required blacks and whites to have separate bathrooms in some areas are widely considered unethical today, however, we do not see women's rights organizations fighting for combined bathrooms or locker rooms. This is because the importance of gender is common sense. Men and women are supposed to be different, and they need one another, not just for the continuation of the human race, but for the fulfilment of our individual purposes. "Orientation" or "preference" do not override "identity" and "purpose."
Christians that oppose homosexual marriage or other violations of the law of chastity are often confronted with the "harm" argument. The idea behind this is that in a free society, an individual should be free to do anything so long as it does not cause harm to themselves or others. Christians might be challenged with questions such as "what did they ever do to you?" or "how do two people loving each other hurt anyone?" The basic challenge to the belief in chastity is that breaking this law does not harm anyone so long as it is practiced by consenting adults. In some cases, harm caused by unchastity is easy to see. Who thinks that broken marriages, costly divorces, and custody battles are positive experiences? Putting a child up for adoption, or the tragedy of abortion might be even more harmful for those that find themselves in such circumstances. More difficult to see is the harm caused by pornography, although men that find themselves addicted to it find themselves dealing with more than annoying pop-ups or expensive media. Perhaps the most elusive harm to see is that caused by the acceptance of homosexual marriage.
Having previously discussed the importance of gender, there is an opportunity cost for those that participate in homosexuality of fulfilling the purposes for which they were given their gender.
Additionally, many homosexuals misconstrue marriage as a right. All states in the US already restrict this so-called right by a variety of other criteria. The number of persons being married has been limited to two individuals for quite some time, effectively prohibiting polygamous unions. There are also age restrictions, which thankfully deny pedophiles the right to have their awful crimes justified. There are restrictions against the relationship of involved parties, so that a brother and sister, even if they feel they are truly in love, are not permitted to marry. A person cannot marry inanimate objects, otherwise, we might have people marrying their motorcycles or their guitars. A person cannot marry non-humans... which means that the crazy cat lady that would like to be eternally bound to her pets cannot legally call her bond a marriage. Homosexuals would like to re-draw the line to allow them to receive marriage, but have put forth no arguments as to why this privilege should be denied to others from which both law and common sense currently protect.
The greatest harm caused by unchastity in any form, whether heterosexual or homosexual in nature, is religious. This is often ignored by those that engage in these practices since these reasons can be seen as the forcing of beliefs on the unwilling. Just because there are those that do not believe that God does not condone these behaviors does not mean that God has not commanded them to be chaste. This is particularly true for those of us in America. An important theme of the Book of Mormon is that this is the promised land. God swore in his wrath and fierce anger that whosever should "...should serve him, the true and only God, or they should be swept off when the fulness of his wrath should come upon them. And now, we can behold the decrees of God concerning this land, that it is a land of promise; and whatsoever nation shall possess it shall serve God, or they shall be swept off when the fulness of his wrath shall come upon them. And the fulness of his wrath cometh upon them when they are ripened in iniquity. For behold, this is a land which is choice above all other lands; wherefore he that doth possess it shall serve God or shall be swept off; for it is the everlasting decree of God. And it is not until the fulness of iniquity among the children of the land, that they are swept off." (Ether 2: 8-10) The Book of Mormon tells the tragic stories of two groups of people that failed to heed the commandments of God, and that he destroyed. It is a witness that God will not endlessly tolerate those that mock his servants and his laws. On individual basis, those that openly fight against him will be cut off from spiritual blessings. On a collective basis, those that openly fight against him invite destruction. I plead with those that disagree with me to avoid attempts to call God's bluff... because he is not bluffing.
Finally, no one knows the harm of unchastity more than Jesus Christ himself. Though he lead a pure and virtuous life, he paid the price for those that have not with his own blood. The pain and anguish were so great that even the only begotten son of God plead with his Father that he might escape the torture... a torture that our sins caused. And yet in spite of our crimes causing him pain, he begs us to come back to him... to believe in his power to heal... to believe that he can free us of our crimes if we will swear to serve him with all our hearts. Even though our mistakes burdened him with unspeakable torment, at the last day, when our Heavenly Father looks at our mistakes, he offers us to be the one to beg the Almighty to forgive us if we have faith in him. I submit that if no other reasons are persuasive, or if the harm of unchastisty is still inconclusive, that Christ has done more than enough to earn a "because I said so" explanation.