The Holy Scriptures are indispensable for so many reasons that one could hardly dare quantify.  Of course it is the burden of all scripture to testify that Jesus is the Christ, the Son of the living God, and that He atoned for the sins of all mankind, thus being the Great Redeemer.  If one were to attempt to identify additional indispensable purposes of the scriptures, one would certainly want to include the containing and dispensing of God’s laws and commandments, that man may be free to follow his Savior unto redemption.  As Elder D. Todd Christopher taught, “The scriptures are the standard for distinguishing truth and error” (General Conference, April 2010).  It is of immanent importance that truth and error be distinguished in relation to God’s commandments.  Not the least of any of His commandments and laws would be the law of chastity, and certainly requiring of clarity.
Elder Christopher explains, “The scriptures, for example, discredit an ancient philosophy that has come back into vogue in our day—the philosophy of Korihor that there are no absolute moral standards, that ‘every man prosper[s] according to his genius, and that every man conquer[s] according to his strength; and whatsoever a man [does is] no crime’ and ‘that when a man [is] dead, that [is] the end thereof’ (Alma 30:17–18).  Alma, who had dealt with Korihor, did not leave his own son Corianton in doubt about the reality and substance of a divine moral code.  Corianton had been guilty of sexual sin, and his father spoke to him in love but plainly: ‘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).”
I have taught before, as so many others before me, that some would happily mistake the term immutable with outmoded.  Outmoded defined is:

Gone out of style; no longer fashionable: not acceptable by present standards; no longer usable; obsolete.

To the contrary immutable is defined:

Unchanging over time or unable to be changed, not mutable; unchangeable; changeless.

The law of chastity is immutable, not outmoded.
With obedience to the law of chastity, like other laws and commandments, come marvelous blessings.
I would never call any of God’s laws outmoded, but by some measures, some of the rules of society and even the rules we find in the various handbooks and scriptures of the Church are not immutable.
When I was a young deacon it was not the accepted standard for young women to wear pants to most youth activities.  Dresses were required at almost all events, and especially dances.  Just a few years before my time blue jeans were not even allowed to be worn by young men at youth activities.  T-shirts for young men or young women were not acceptable at any kind of dance until after I reached adulthood.  The same standards were very similar outside of the Church as well.  These were not immutable laws, they were simply the standard for the day, nevertheless enforced to all who wanted to participate.  And blessings came to those who were obedient to the rules set down by their leaders.
There was nothing wrong with those rules in their time, yet that doesn’t mean that a young lady appropriately wearing a pair of pants today to a youth activity is in anyway inappropriate, or that she will be denied blessings as a result of doing so.  Some of these rules become outmoded, that is why we often have changes in policies and even in the handbooks of the Church.  Yes, at times clarifications need to be made, but often we make minor changes because the circumstances of the day are different from those of prior days.  When it comes to the adjusting of a Church policy because of some type of non-immutable societal correction, we simply make the adjustment and move obediently on knowing that the important things are the immutable laws taught us by the Lord and the teachings and counsels that our living prophet and other Church leaders, even the whisperings of the Holy Ghost, provide today.
On the other hand, there are immutable unchanging laws that need to be regarded at all times, never to be considered outmoded, and the law of chastity is near foremost among these.
In the gospel library under the heading “What Is the Law of Chastity?” we define:

The law of chastity requires that sexual relations be reserved for marriage between a man and a woman.

We also read, “In addition to reserving sexual intimacy for marriage, we obey the law of chastity by controlling our thoughts, words, and actions.  Jesus Christ taught, ‘Ye have heard that it was said by them of old time, Thou shalt not commit adultery: but I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart’ (Matthew 5:27–28).”
Of the serious nature of the law of chastity to God, Elder Jeffrey R. Holland in the October 1998 General Conference taught, “Clearly among His greatest concerns regarding mortality are how one gets into this world and how one gets out of it.  He has set very strict limits in these matters. … Human intimacy is reserved for a married couple because it is the ultimate symbol of total union, a totality and a union ordained and defined by God. … Marriage was intended to mean the complete merger of a man and a woman. … This is a union of such completeness that we use the word seal to convey its eternal promise.”
The law of chastity is indeed an immutable law of God, it is unchanging and ever the same, ever relevant.  No matter what temptation, society or social pressure dictates, no matter what the actions (the sins) of politicians, celebrities, mentors, athletes, artists, idols, friends, causes, leaders or loved ones, the law of chastity will never become outmoded to God, nor to His people.  The law of chastity is eternal and is the key to our happiness today and in the eternities.  As Alma the Younger declared to his repenting son Corianton, “wickedness never was happiness” (Alma 41:10), so I declare today, that true happiness, true joy, is found in the keeping of God’s immutable laws, and most especially in this law at the very heart of God’s great plan of happiness for us.  May we ever remember the sacred nature of the power of procreation, the supernal joy of intimacy in splendor between husband and wife, and do nothing to frustrate our loving Father’s blessed plan for our happiness.  Thanks be to the Savior for His atoning sacrifice, and our hope, in the name of Jesus Christ, amen.