Exodus 40:15

And thou shall anoint them as thou didst anoint their father,.... For Aaron was first anointed, and then his sons:

that they may minister unto me in the priest's office; which they might not do before their anointing, though separated for it, and called unto it:

for their anointing shall surely be an everlasting priesthood throughout their generations; that is, this ceremony of anointing was to be used in all ages at the investiture of the high priest with his office, until the Messiah should come, who would put an end to the Aaronic priesthood; for not common priests, only the successors of the high priest, were anointed in later times; this present unction serving for all the priests that should follow in successive generations, so long as the priesthood continued.