8 Then Moses placed the chestpiece on Aaron and put the Urim and the Thummim inside it. 9 He placed the turban on Aaron's head and attached the gold medallion-the badge of holiness-to the front of the turban, just as the Lord had commanded him. 10 Then Moses took the anointing oil and anointed the Tabernacle and everything in it, making them holy. 11 He sprinkled the oil on the altar seven times, anointing it and all its utensils, as well as the washbasin and its stand, making them holy. 12 Then he poured some of the anointing oil on Aaron's head, anointing him and making him holy for his work.
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.