"...AND HE SHALL NOT DIE." (Shemos 28:35)
Even though [Aharon] did not come [for the service in the Sanctuary] of his own volition, but to fulfill the command of Hashem (Vayikra 163), yet the pious intention is not sufficient to protect one that enters near to Hashem. Thus, at the Giving of the Torah, despite the enthusiastic willingness of the nation, they were warned repeatedly against coming too near to Mount Sinai (see above 19:21).
The Mitzvos must be performed not only with Love but also with the greatest Awe. The lack of Fear of Hashem is worse than the failure to perform the Mitzvah; for the lack of proper vestments to honor Hashem is punishable by death (at the hands of Heaven), whereas no death is foretold for the neglect to perform the service.
The Mitzvos must be performed not only with Love but also with the greatest Awe
"AND MAKE FOR THEM BREECHES OF LINEN. (28:42)
This garment was also among the vestments of the Cohen Gadol, who in addition to the four garments (head-covering, tunic, girdle, breeches) wore also the golden forehead-plate, the Me’il, the Choshen and the Efod. Neither he or the others wore shoes.
This is reminiscent of Hashem’s admonition to Moshe: “Remove your shoes from your feet, for the place upon which you stand is holy soil” (3:5). Despite the “glory and the splendor” (28:2) of those that officiated before Hashem, yet they were required to demonstrate their humility in the service of the Master Oust as the Cohen Gadol, in all his splendor, nevertheless wore an apron like a humble servant (see 28:21).
The barefoot Cohen Gadol was never able to become arrogant, despite the golden crown with the name of Hashem and despite the precious gems and costly vestments; for he needed but to glance down at his bare feet — A Nation is Born