Exodus 40:15

“And thou shall anoint them as thou didst anoint their father, etc.] 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…”

“anoint them, as thou didst anoint their fathers--The sacred oil was used, but it does not appear that the ceremony was performed exactly in the same manner; for although the anointing oil was sprinkled over the garments both of Aaron and his sons (Exo 29:21; Lev 8:30), it was not poured over the heads of the latter. This distinction was reserved for the high priest (Exo 29:7; Lev 8:12; Psa 133:2).”

“Their anointing shall be an everlasting priesthood - A seal that their priesthood shall continue as long as the Jewish polity lasts. He signifies that this unction should be sufficient for all succeeding priests. None were afterwards anointed but the high - priests. Exodus 40:34”

“everlasting: Exo 12:14, Exo 30:31, Exo 30:33; Num 25:13; Psa 110:4; Heb 5:1-14, Heb 7:3, Heb 7:7, Heb 7:17-24; Heb. 8:1-10:39 Exodus 40:16”