Explains the Ohr HaChaim, HaShem commanded us to fashion these eight garments in order to atone for sins and blemishes that our human failings cause on high. Why then, asks the Ohr HaChaim, did HaShem only command Aharon and not Moshe to wear these garments?
Chazal say (Arachin 16a) that the eight garments atone for eight types of sins that Bnei Yisrael transgressed. The Kohen, whose job is to serve together with his sons and atone for all of Klal Yisrael, is therefore commanded to wear these garments, whereas Moshe, who only served once during the seven-day inaugural period called Yemei HaMiluim, did so in order to atone solely for Aharon and his sons, to prepare them to serve before HaShem. Because he was not atoning for all of Klal Yisrael, Moshe did not need these garments.
