All of them are spirits on a divine mission, sent to serve those who are about to inherit salvation, aren't they?

No one takes this honor upon himself but he is called to it by God, just as Aaron was.

Now if perfection could have been attained through the Levitical priesthood for on this basis the people received the Law what further need would there be to speak of appointing another kind of priest according to the order of Melchizedek, not one according to the order of Aaron?

which had the gold altar for incense and the Ark of the Covenant completely covered with gold. In it were the gold jar holding the manna, Aaron's staff that had budded, and the Tablets of the Covenant.