II.5. On priests.
What is the foundation of the priesthood or from which founder did the order of pontiffs arise in this world? Clearly Aaron was the beginning of the priesthood. Although Melchizedek offered sacrifice prior to him and Abraham, Isaac, and Jacob after him - these men did so by spontaneous will, not by the authority of priesthood. (2) In addition, Aaron was the first one in the Law to accept the name of priest, and the first to offer sacrifices, adorned with the distinct priestly stole. [...]
Here follows the quotation from Exod 29:4-9.
(3) In this place it ought to be considered that Aaron had been the high priest, that is, the bishop. His sons had ministered beforehand as a type of the presbyters. They were the sons of Aaron and priests themselves, to whom the Levites had rightly been bound to minister as also to the high priest. But there was another difference between Aaron the high priest and the sons of Aaron, who themselves were also priests: Aaron, over the tunic, received the poderem, the holy stole, and the gold crown miter and the gold bracelet and the ephod, and the other things that were mentioned above. The sons of Aaron, however, over the linen tunics had only cinctures and tiaras, when they were offering sacrifice to God. [...]
Here follows the typology according to which Aaron is a type of bishop, his son of presbyters, and Moses of Christ.
(5) Thus far concerning the first priests in the Old Testament. In the New Testament, however, after Christ the order of priesthood began with Peter. For to him the pontificate in the church of Christ was given first. Thus the Lord said to him: "you are Peter, and on this rock I will build my church, and the gates of hell will not prevail against it. I will give you the keys of the kingdom of heaven" [Matt 16:18-19]. He was therefore the first to receive the authority of binding and loosing, and the first to bring people to faith by the power of his preaching. And since the other apostles also became equal sharers with Peter in honor and authority, they also preached the gospel, dispersed throughout the whole world. (6) Coming after them, there succeeded the bishops, who have been set up throughout the world in the seats of the apostles. They are not chosen now from descent by flesh and blood, which was done first according to the order of Aaron, but by each one's merit, which divine grace has bestowed on him. [...]
Here follows the quoatation from 1 Sam 2:30.
(7) There are four kinds of apostles: the first is from God, as in the case of Moses. The second is through man and God, as Joshua. The third is only through man, since in these times many are called into the priesthood because of the approval of people and authorities. The fourth, however, is a category unto itself, as of pseudo-prophets and pseudo-apostles. As for the name of apostles, however, in the Latin language apostles is translated as "sent" because Christ sent them to evangelize for the illumination of all peoples.
(trans. Knoebel 2008: 71-73, slightly altered)