The Torah devotes an entire Parsha to the preparation of the priestly vestments. Indeed, the Torah gives more space to the priestly vestments than to the holy vessels which were actually used in the Mishkon. Although the priestly vestments were not an actual part of the service, the service could be performed only when the Kohein was wearing them. It seems apparent that the vestments performed a sublime role. The Chizkuni explains that these garments constituted a sanctified beauty.
Clothing is a symbol of man's higher nature.
By distinguishing between man and animals, clothes give a man special dignity. The Koheinim were, therefore, required to dress in accordance with their exalted position, reflective of man's higher calling. Man's essence must mirror these qualities. The moral attributes and character refinement manifested by the Kohein should be inherent throughout his entire essence. It should be reflected externally as well.