Matthew Poole and continuators on Exodus 40:15

15 And thous shalt anoint them, as thou didst anoint their father, that they may minister unto me in the priests office: for their anointing shall surely be an everlasting priest-hood , throughout their generations.

(i. e.) A sign or seal that their Priesthood shall continue as long as their policy lasts, till the coming of the Messias. He signifies that this unction should be sufficient for all succeeding Priests, they should not need to be anointed again, except the successive High-priests. See Exod. 29. 7, 29. Levit. 4. 3. and 16. 32. and 21. 10.