Deuteronomy 32:50,51

And die in the mount... as Aaron thy brother died in mount Hor... because ye trespassed against me. — It may be asked why Moses and Aaron should both have been made to ascend a mountain to die. I believe a clue to the reason may be found in the words and act which constituted their transgression. They were bidden to speak to the rock in Kadesh, and they struck it. The words which Moses used on that occasion were, “Hear now, ye rebels; must we fetch you water out of this cliff (Selagh)?” The last words of the sentence are emphatic; and the rock is described as a cliff, not by the name given to the Rock in Horeb (Tzûr). The emphasis laid upon these words has been much discussed by Jewish commentators, though it escapes English readers. I suspect that the mistake Moses and Aaron made, in thinking it needful to strike the cliff, also led them to think it necessary to ascend it, instead of gathering the congregation together beneath it, and speaking to it from below. This view harmonises with the spiritual significance of the act. The smitten Rock in Horeb was Christ; the Cliff not to be smitten in Kadesh pointed also to Christ, ascended now, needing only the prayer of faith to call down all that He will give. And so Moses himself taught, in some of his latest words. “It is not in heaven that thou shouldest say, Who shall go up for us to heaven, and bring it unto us?... But the word is nigh thee, in thy mouth.”

The impatient words of Moses, after toiling up the cliff with his brother Aaron, had to be recompensed by their ascending mount Hor and mount Nebo to die. Moses, as the more responsible of the two, had to ascend on each occasion, for his brother’s death and for his own. The remembrance of his brother’s death in the Lord may well have comforted Moses in the prospect of his own.