Numbers 20:26

[His] vestments. In the vestments of the kehunah Gedolah, he dressed him, and then removed them from him, in order to place them on his son in his presence. He said to him, “Enter the cave.” He entered. He saw a bed made ready and a candle burning. He said, “Go up on the bed.” He went up. “Extend your hands.” He extended them. “Close your mouth.” He closed it. “Shut your eyes.” He shut them. Moshe at once desired to die such a death. This is why it was said to him, “The way your brother Aharon died”— The death which you desired.

And thou shalt strip Aharon of his vestments, the adornment (glory) of the priesthood, and put them on Elazar his son; but Aharon shall be gathered, and die there.

AND STRIP AARON OF HIS GARMENTS. These are the garments [reserved only] for the High Priest, with which Eleazar his son was now appointed [High Priest in his stead]. It is likely that when Aaron came down from offering the Daily Whole-offering, and burnt the incense and kindled the lamps, Moses took him up to Mount Hor whilst he was still dressed in the garments of the [High] Priest, and [then] he stripped him of them. And according to the plain meaning of Scripture [the verse is to be interpreted: And strip Aaron of his garments in order to] put on him the shrouds of a dead man which he had prepared for him, and then he stripped Eleazar of his ordinary clothes and put the sacred garments upon him, as he did to him on the day of initiation. And according to the Midrashic interpretation of our Rabbis, 1:6. various miracles occurred in connection with these garments. Thus they said: “How could Moses strip Aaron of his garments in their proper order? Are not the upper ones always on top, and the lower ones always underneath? But G-d did miraculous deeds for Aaron at the time of his death, even more so than during his lifetime. Thus Moses put Aaron upon the rock and stripped him of the priestly garments, and [alternative] celestial garments clothed themselves [upon him] underneath them. robe, he was covered with a corresponding celestial garment underneath his tunic [which was the lower garment directly on his body]. Moses could then proceed to remove the tunic [which was now above the celestial “upper” robe, thereby fulfilling the Divine command of stripping Aaron of his garments “in their proper order.” As he removed the tunic, a corresponding celestial tunic likewise clothed itself underneath the celestial robe. This interpretation of the Torath Kohanim is based upon Malbim’s commentary. And he put them upon Eleazar his son. But how could Moses put the garments upon Eleazar in their proper order? [We must say that this was not natural], but that G-d bestowed a great honor upon Aaron at the time of his death, even more so than during his lifetime, in that celestial garments first [miraculously] clothed themselves underneath [the other garments], and then Moses stripped Aaron of the priestly garments in their proper order, and [also] put them on Eleazar in their proper order.” So it is taught in the Torath Kohanim. 1:6.

והפשט אהרן את בגדיו, the garments that were exclusively those of a High Priest, i.e. those in addition to the garments worn by the ordinary priest.

והלבשתם את אלעזר, who was already wearing the standard four garments which every priest wore. As a result, Aaron would remain wearing the basic four garments worn by every priest. It is precisely these four garments which he would wear any time he had occasion to enter the Holy of Holies, so that he in no way was deprived of status by not wearing the garments which were meant only for his image among his peers, not for his image when facing G’d. In fact, basically, what he remained with were the kind of garments angels appear in when they appear to human beings.