Exodus 40:15

Thou shalt anoint them, as thou didst anoint their father. — By the narrative of Leviticus 8, it would seem that Aaron’s sons were not anointed in the same way as himself. He had the oil poured over his head (Leviticus 8:12; Psalms 133:2). They were merely sprinkled with a mixture of oil and blood (Leviticus 8:30). The difference implied a lower degree of official holiness.

Their anointing shall surely be an everlasting priesthood. — The Jewish commentators maintain that the one anointing of the sons of Aaron sufficed for all time, and was not repeated in the case of any subsequent priests, who became fully possessed of the sacerdotal office without it. Each high priest was, on the contrary, inducted into his office by anointing, whence the high priest came to be spoken of as “the anointed priest (Leviticus 4:3; Leviticus 4:5; Leviticus 4:16; Leviticus 21:12, &c.).