Pope St. Leo the Great ca. 400-461
For it is He of whom it is prophetically written, You are a priest for ever after the order of Melchizedeck , that is, not after the order of Aaron, whose priesthood descending along his own line of offspring was a temporal ministry, and ceased with the law of the Old Testament, but after the order of Melchizedeck, in whom was prefigured the eternal High Priest. And no reference is made to his parentage because in him it is understood that He was portrayed, whose generation cannot be declared. And finally, now that the mystery of this Divine priesthood has descended to human agency, it runs not by the line of birth, nor is that which flesh and blood created, chosen, but without regard to the privilege of paternity and succession by inheritance, those men are received by the Church as its rulers whom the Holy Ghost prepares: so that in the people of God’s adoption, the whole body of which is priestly and royal, it is not the prerogative of earthly origin which obtains the unction , but the condescension of Divine grace which creates the bishop. (Sermons 3.1)