I will sanctify … the altar. See Le Exodus 9:24, where we learn that on the first occasion of Aaron's offering sacrifice upon the brazen altar, "there came a fire out from before the Lord, and consumed upon the altar the burnt offering and the fat."
Thus the altar had its miraculous sanctification, as well as the tabernacle, and was not merely consecrated by human instrumentality. I will sanctify also both Aaron and his sons. It would seem to follow, by parity of reasoning, that here also something more is intended than had been accomplished by the rites of consecration.
The verb is in the future—"I will sanctify"—and must allude to something which has not yet taken place. Probably, sanctification of the spirit is intended—that Divine influence upon the heart which alone makes men really and truly "holy."
(Compare Le Exodus 21:8, Exodus 21:15; Exodus 22:9, Exodus 22:16.) But in this ease the promise must have been conditional. God would sanctify them so far as they would allow him.