The investiture, as also the anointing, of the sons of Aaron, followed the robing and anointing of Aaron. We read (ver. 13): "Moses brought Aaron's sons, and clothed them with coats, and girded them with girdles, and bound head-tires upon them; as the Lord commanded Moses."
To the three articles of their attire here mentioned, must be added the "linen breeches" (Exod. xxviii. 42, 43); so that they also, in the several parts of their official vestments, bore the number four, the signature of the creaturely, as represented in the tabernacle. All was of pure white linen, signifying the holiness and righteousness of those who should act as priests before God. So once and again in the Apocalypse, the same symbol is used to denote the spotless holiness and righteousness of the blood-bought saints, who are made "a kingdom and priests" unto God; as, for instance, it is said of that same holy body, symbolised as the bride of the Lamb, that "it was given unto her that she should array herself in fine linen, bright and pure: for the fine linen is the righteous acts of the saints" (Rev. xix. 8).
The Anointing.
viii. 10-12.
"And Moses took the anointing oil, and anointed the tabernacle and all that was therein, and sanctified them. And he sprinkled thereof upon the altar seven times, and anointed the altar and all its vessels, and the laver and its base, to sanctify them. And he poured of the anointed oil upon Aaron's head, and anointed him, to sanctify him."
Next in order came the anointing, first of the tabernacle and all that pertained to its service, and then the anointing of Aaron.
The anointing oil was made (Exod. xxx. 22-33) with a perfume of choice spices, their number, four, the sacred number so constantly recurring in the tabernacle. To make or use this oil, except for the sacred purposes of the sanctuary, was forbidden under penalty of being cut off from the holy people. The purpose of the anointing of the tabernacle and all within it, is declared to be its consecration thereby to the service of Jehovah. The altar, as a place of special sanctity, the place where God had covenanted to meet with Israel, was anointed seven times. For the number seven, compounded of three, the signet number of the Godhead, and four, the constant symbol of the creaturely, is thus by eminence the sacred number, the number, in particular, which is the sign and reminder of the covenant of redemption; and so here it is with special meaning that the altar, as being the place where God had specially covenanted to meet with Israel as reconciled through the blood of atonement, should receive a sevenfold anointing.
After this, the anointing oil was poured on the head of Aaron, to sanctify him.
As to the meaning of this part of the symbolic service, there is little room for doubt. The "anointing" is said to have been "to sanctify" or set apart to the service of Jehovah him that was anointed. And, inasmuch as oil, in the Holy Scriptures, is the constant symbol of the Holy Spirit, it is taught hereby that consecration is secured only through the anointing with the Holy Ghost.