Notes on Aaronic and Melchizedek Priesthoods.
The law of Moses and the priesthood went together. All the people without exception were sinners, subject to the law's condemnation, and were thus in need of a priestly system to mediate between them and God. The Aaronic priesthood was imperfect, but the Melchizedek priesthood was perfect (as implied in Hebrews 7). The announcement of the coming one who would be a priest forever (Ps.110:4) was written midway in the history of the Levitical priesthood, which could only mean that the existing system was to give way to something better. Jesus came from the non-priestly tribe of Judah, but became a priest forever in the Melchizedek order. There is no indication in the scripture that any other person held this high priesthood.