Hebrews 7:11-14

So if the priesthood of Levi, on which the law was based, could have achieved the perfection God intended, why did God need to establish a different priesthood, with a priest in the order of Melchizedek instead of the order of Levi and Aaron? And if the priesthood is changed, the law must also be changed to permit it. For the priest we are talking about belongs to a different tribe, whose members have never served at the altar as priests. What I mean is, our Lord came from the tribe of Judah, and Moses never mentioned priests coming from that tribe.