And thou shalt bring Aaron and his sons unto the door of the tabernacle of the congregation, and wash them with water.
Bring Aaron and his sons unto the door of the tabernacle ... and wash them. This ceremony, as Hengstenberg remarks, was observed also in Egypt, where the priests were purified with water before they assumed the sacerdotal robes, and there was a general but very striking similarity of the sacerdotal institutions among the Egyptians and Israelites. The whole ceremony of investiture, the anointing oil poured on them after their equipment in the official robes, the cap, the crown, all were the same. But there were also marked differences in the ritual of the tabernacle, which will be noticed as they occur.
Verse 15. And thou shalt anoint them, as thou didst anoint their father. 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 (Exodus 29:21; Leviticus 8:30), it was not poured over the heads of the latter. This distinction was reserved for the high priest (Exodus 29:7; Leviticus 8:12; Psalms 133:2).
For their anointing shall surely be an everlasting priesthood throughout their generations - i:e., so long as the national polity should last, and until the Aaronic priesthood be superseded by the advent of Messiah. Not only so, but as the priestly office was hereditary in the house of Aaron, the first consecration was sufficient for all future priests: none of the succeeding ones were anointed, with the exception of the high priests only (Exodus 29:29; Leviticus 4:3; Leviticus 16:32; Leviticus 21:10).