8 And he put the priest's bag on him, and in the bag he put the Urim and Thummim. 9 And on his head he put the head-dress, and in front of the head-dress the plate of gold, the holy crown, as the Lord gave orders to Moses. 10 And Moses took the holy oil and put it on the House and on all the things in it, to make them holy. 11 Seven times he put oil on the altar and on all its vessels, and on the washing-basin and its base, to make them holy. 12 And some of the oil he put on Aaron's head, to make him holy.
Matthew Henry's Commentary on Leviticus 8:8-12
Commentary on Leviticus 8:1-13
(Read Leviticus 8:1-13)
The consecration of Aaron and his sons had been delayed until the tabernacle had been prepared, and the laws of the sacrifices given. Aaron and his sons were washed with water, to signify that they ought to purify themselves from all sinful dispositions, and ever after to keep themselves pure. Christ washes those from their sins in his own blood whom he makes kings and priests to our God, Hebrews 10:22. The anointing of Aaron was to typify the anointing of Christ with the Spirit, which was not given by measure to him. All believers have received the anointing.