The LORD commanded the children of Israel to make special garments for the priests to wear while they officiated in the Tabernacle: "You shall make holy garments for Aaron your brother, for glory and for beauty"(Exodus 28:2). The garments of the priesthood were set apart for the purpose of serving God in the Tabernacle. They were not to be used for any other purpose.
Holiness does not mean that there is some kind of a mystical goodness attached to the object, person or place described as holy. It simply means that God does not want it used for anything other purposes than His own. The opposite of something holy is something normal.
Not only were the priest's clothes holy garments, they were vestments for glory. The Hebrew word translated "glory" is kivod, (כבוד). It also means "honor." Its root meaning is closely connected with the Hebrew word for "heavy." To treat something lightly would be the opposite of glorifying it. Maimonides points out that the priest's garments were not meant to glorify the priests who wore them. Instead, the priests' garments reminded the people of God's greatness.
The laws of the priestly garments teach some important lessons about clothing. For example, they teach that the way we dress matters to God. Clothing can bring honor or dishonor to God.
In many churches, and even in some synagogues, it has become popular to dress casually. Typically people dress better when they are going out to an expensive restaurant than they do when they attend worship services of the Most High. Even in Messianic assemblies people rarely dress their best for keeping the Sabbath. Jeans and T-shirts on Sabbath mornings? Shorts on Yom Kippur? Immodest, body-revealing clothing is flaunted even in the presence of the holy Torah scroll.
In modern Western culture, it has become common to regard dress and apparel as inalienable rights that are essential expressions of the individual. What is more, we have adopted some sort of assumed piety in dressing down. The reasoning proceeds along these lines: God does not look at the outside. God looks at the heart. Therefore, the outside should not matter.
Ironically, those who wear blue jeans and T-shirts to worship services seem to regard themselves more intrinsically spiritual than the "stiffs" who still dress formally, because they assume that their casual dress reflects a more genuine heart.
The laws of the priestly vestments prove that God looks at the outside as well as the inside, and He is concerned for how His people present themselves in the eyes of the world. The way we dress often reveals what's going on inside us. It also reflects on God. To dress disrespectfully on His holy days in His holy houses of worship is to disrespect Him.