Chapter 21 — Part II: The Sacraments — Holy Orders
Section 53. This distinction of the priesthood can be seen even in the Old Law. That David spoke of the internal priesthood, we have just shown. On the other hand, everyone knows the many and various precepts given by the Lord to Moses and Aaron regarding the external priesthood. Along with this He appointed the whole tribe of Levi to the ministry of the Temple, and He forbade by law that anyone belonging to another tribe should dare to intrude himself into that function. Hence it was that King Ozias was afflicted with leprosy by the Lord for having usurped the sacerdotal ministry, and had to suffer grave chastisements for his arrogance and sacrilege.