Hebrews 7:8-12

8In the case of the Levites, mortal men collect the tenth; but in the case of Melchizedek, it is affirmed that he lives on. 9And so to speak, Levi, who collects the tenth, paid the tenth through Abraham. 10For when Melchizedek met Abraham, Levi was still in the loin of his ancestor.

11Now if perfection could have been attained through the Levitical priesthood (for on this basis the people received the law), why was there still need for another priest to appear—one in the order of Melchizedek and not in the order of Aaron? 12For when the priesthood is changed, the law must be changed as well.