Or HaChaim on Numbers 20:26/אור החיים על במדבר כ׳:כ״ו

1 והפשט את אהרן את בגדיו, "and strip Aaron of his garments." The fact that the Torah wrote the word את twice, both in connection with Aaron and in connection with his garments suggests that there were two separate "strippings." We might have thought that the garments that Aaron was to be stripped of were the priestly garments, not his personal clothing. This is why the Torah also had to write: "strip Aaron" to indicate that he was to be stripped also of his personal garments. It was only concerning the priestly garments that the Torah continued: והלבשתם את אלעזר בנו, "and put them on his son Eleazar. Had the Torah merely written והפשט אהרן את בגדיו, I would not have had the extra word את from which I could have deduced the proper meaning of the verse. On the other hand, if the Torah had only written והפשט אהרן בגדיו (without either word את), I would have simply understood that Aaron was to be stripped naked, and the words את בגדיו would have become meaningless.

2We may also interpret these words slightly differently. The words הפשט את אהרן refer only to his personal clothing. The Torah added the words את בגדיו to teach us that he would immediately be robed in different garments. This is what the Yalkut Shimoni on our verse had in mind when the author wrote: "While Aaron was being undressed he was immediately enveloped by the clouds of glory." As a result, Aaron was never in a state of undress even while Moses undressed him as parts of the clouds of glory enveloped any part of his body from which Moses removed his clothing.