Hebrews 7:9-12

9One might even say that Levi, who collects the tenth, paid the tenth through Abraham, 10because when Melchizedek met Abraham, Levi was still in the body of his ancestor. 11If perfection could have been attained through the Levitical priesthood—and indeed the law given to the people established that priesthood—why was there still need for another priest to come, one in the order of Melchizedek, not in the order of Aaron? 12For when the priesthood is changed, the law must be changed also.