I think he covers it pretty well:
http://speeches.byu.edu/reader/reader.php?id=8555&x=55&y=2
3. Sacred Places and Occasions
Lets now consider for a moment the matter of sacred places and events. Speaking through the prophet Ezekiel, the Lord criticized Israels priests for failing to teach respect for the sacred nature of certain activities and places:
Her priests have violated my law, and have profaned mine holy things: they have put no difference between the holy and profane, neither have they shewed difference between the unclean and the clean, and have hid their eyes from my sabbaths, and I am profaned among them. [Ezekiel 22:26]
Much of what the Lord was talking about had to do with the temple. There is also reference to the Sabbath. We are used to thinking of our temples and meetinghouses as dedicated to the Lord, as sacred space. On each temple building are found, as a sober reminder, the words
Holiness to the Lordthe House of the Lord. A sense of the sacred should lead us to act and speak with reverence in and around these buildings. It would lead us to dress a certain way when we are there.
We spoke of immodest dress as dishonoring the body, Gods most sacred creation. I speak now of immodest, casual, or slovenly dress and grooming that in particular times and places mocks the sacredness of what is taking place or of the place itself.
Let me give you an example. A while back a young woman from another state came to live with some of her relatives in the Salt Lake City area for a few weeks. On her first Sunday she came to church dressed in a simple, nice blouse and knee-length skirt set off with a light, button-up sweater. She wore hose and dress shoes, and her hair was combed simply but with care. Her overall appearance created an impression of youthful grace.
Unfortunately, she immediately felt out of place. It seemed like all the other young women her age or near her age were dressed in casual skirts, some rather distant from the knee; tight T-shirtlike tops that barely met the top of their skirts at the waist (some bare instead of barely); no socks or stockings; and clunky sneakers or flip-flops.
One would have hoped that seeing the new girl, the other girls would have realized how inappropriate their manner of dress was for a chapel and for the Sabbath day and immediately changed for the better. Sad to say, however, they did not, and it was the visitor who, in order to fit in, adopted the fashion (if you can call it that) of her host ward.
It is troubling to see this growing trend that is not limited to young women but extends to older women, to men, and to young men as well. Years ago my ward in Tennessee used a high school for church services on Sundays while our chapel, which had been damaged by a tornado, was being repaired. A congregation of another faith used the same high school for their worship services while their new chapel was being constructed.
I was shocked to see what the people of this other congregation wore to church. There was not a suit or tie among the men. They appeared to have come from or to be on their way to the golf course. It was hard to spot a woman wearing a dress or anything other than very casual pants or even shorts. Had I not known that they were coming to the school for church meetings, I would have assumed that there was some kind of sporting event taking place.
The dress of our ward members compared very favorably to this bad example, but I am beginning to think that we are no longer quite so different as more and more we seem to slide toward that lower standard. We used to use the phrase Sunday best. People understood that to mean the nicest clothes they had. The specific clothing would vary according to different cultures and economic circumstances, but it would be their best.
It is an affront to God to come into His house, especially on His holy day, not groomed and dressed in the most careful and modest manner that our circumstances permit. Where a poor member from the hills of Peru must ford a river to get to church, the Lord surely will not be offended by the stain of muddy water on his white shirt.
But how can God not be pained at the sight of one who, with all the clothes he needs and more and with easy access to the chapel, nevertheless appears in church in rumpled cargo pants and a T-shirt? Ironically, it has been my experience as I travel around the world that members of the Church with the least means somehow find a way to arrive at Sabbath meetings neatly dressed in clean, nice clothes, the best they have, while those who have more than enough are the ones who may appear in casual, even slovenly clothing.
Some say dress and hair dont matterits whats inside that counts. I believe that truly it is whats inside a person that counts, but thats what worries me. Casual dress at holy places and events is a message about what is inside a person. It may be pride or rebellion or something else, but at a minimum it says, I dont get it. I dont understand the difference between the sacred and the profane. In that condition they are easily drawn away from the Lord. They do not appreciate the value of what they have. I worry about them. Unless they can gain some understanding and capture some feeling for sacred things, they are at risk of eventually losing all that matters most. You are Saints of the great latter-day dispensationlook the part.
These principles apply as well to activities and events that are themselves sacred or are related to things that deserve reverencepriesthood ordinances, for example: baptisms, confirmations, ordinations, administration of the sacrament of the Lords Supper, blessings of the sick, and so forth. The Doctrine and Covenants tells us that in the ordinances of the priesthood the power of godliness is manifest (D&C 84:20).
Alma says that
these ordinances were given . . . that thereby the people might look forward on the Son of God, it being a type of his order, or it being his order, and this that they might look forward to him for a remission of their sins, that they might enter into the rest of the Lord. [Alma 13:16]
I appreciate both those who perform these ordinances and those who witness or receive them when they show respect for the priesthood and the sacred nature of what is occurring.
I appreciate priests, teachers, and deacons who wear dress shirts and ties to officiate in the administration of the sacrament.
I appreciate men who put on a shirt and tie, when the circumstances permit, to bless the sick. I appreciate those who attend the ordination of a man to a priesthood office who dress in their Sunday best no matter what day or where the ordination takes place. They are all demonstrating an appreciation and respect for God and for the event. They are demonstrating a sense of the sacred.
Just as it is sacred when a life comes into being, so it is a sacred time when mortal life comes to an end. And I believe the same is true with respect to the most important act that can occur in lifemarriage, especially eternal marriage. For this reason it is disconcerting to see how people are becoming careless, even irreverent and disrespectful, in speech, dress, and conduct when they participate in events related to death and marriage.
Some funeral services become occasions for lightmindedness and inappropriate humor. Personal remembrances, quite appropriate in moderation, can occupy an hour or two while the Atonement and Resurrection of the Lord and His plan of salvation receive only a passing mention, if any.
Occasionally at weddings and often at wedding receptions, people arrive in very casual clothing. It is as if they cannot be bothered to clean up from their work or recreation of that day. By their dress they are saying that the marriage they have been invited to honor is of little significance. Recently I read a note from a man who was urging his companions to wear a coat and tie when they appeared together at a public event honoring their organization and what it had accomplished. Their service was civic, not religious in nature, and we would not term it sacred, but he understood the principle that some things deserve respect and that our manner of dress is a part of that expression. He said he was going to dress more formally not because Im important, but because this occasion is so important. His comment states an important truth. It is really not about us. Acting and dressing in a way to honor sacred events and places is about God.