Treasury of Scripture Knowledge
"And you, bring near to you your brother Aaron and his sons with him from among the Israelites, so that they may minister as my priests -- Aaron, Nadab and Abihu, Eleazar and Ithamar, Aaron's sons.
He has brought you near and all your brothers, the sons of Levi, with you. Do you now seek the priesthood also?
But you and your sons with you are responsible for your priestly duties, for everything at the altar and within the curtain. And you must serve. I give you the priesthood as a gift for service; but the unauthorized person who approaches must be put to death."
And no one assumes this honor on his own initiative, but only when called to it by God, as in fact Aaron was.
So if perfection had in fact been possible through the Levitical priesthood -- for on that basis the people received the law -- what further need would there have been for another priest to arise, said to be in the order of Melchizedek and not in Aaron's order?