Moses had time to take off the priestly garments, which were the insignia
of office and to put them on Eleazar, and then, when all was ready, Aaron
simply ceased to breathe at the precise moment when it was convenient for
Moses to have him die, for the policy of Moses evidently demanded that
Aaron should live no longer. Under the conditions of the march Moses was
evidently preparing for his own death, and for a complete change in the
administration of affairs. Appreciating that his leadership had broken
down and that the system he had created was collapsing, he had dawdled as
long on the east side of the Jordan as the patience of the congregation
would permit. An advance had become inevitable, but Moses recognized his
own inability to lead it. The command had to be delegated to a younger man
and that man was Joshua. Eleazar, on the other hand, was the only
available candidate for the high priesthood, and Moses took the
opportunity of making the investiture on Mount Hor. So Aaron passed away,
a sacrifice to the optimism of Moses. Next came the turn of Moses himself.
The whole story is told in Deuteronomy. Within, probably, something less
than a year after Aaron's death the "Lord" made a like communication to
Moses.

"Get thee up ... unto Mount Nebo, which is in the land of Moab, that is
over against Jericho;

"And die in the Mount whither thou goest up, and be gathered unto thy
people; as Aaron, thy brother died in Mount Hor;

"Because ye trespassed against me among the children of Israel at the
waters of Meribah-Kadesh, in the wilderness of Zin, because ye sanctified
me not in the midst of the children of Israel.

"And Moses went up from the plains of Moab unto the mountain of Nebo, ...