HKB
this belongs to the perfection of charity, as stated above (A. 2, ad 3). Therefore it would seem that parish priests and archdeacons also are in the state of perfection.
On the contrary, Dionysius says (Eccl. Hier. v): "The order of pontiffs is consummative and perfecting, that of the priests is illuminative and light-giving, that of the ministers is cleansing and discretive." Hence it is evident that perfection is ascribed to bishops only.
I answer that, In priests and deacons having cure of souls two things may be considered, namely their order and their cure. Their order is directed to some act in the Divine offices. Wherefore it has been stated above (Q. 183, A. 3, ad 3) that the distinction of orders is comprised under the distinction of offices. Hence by receiving a certain order a man receives the power of exercising certain sacred acts, but he is not bound on this account to things pertaining to perfection, except in so far as in the Western Church the receiving of a sacred order includes the taking of a vow of continence, which is one of the things pertaining to perfection, as we shall state further on (Q. 186, A. 4). Therefore it is clear that from the fact that a man receives a sacred order a man is not placed simply in the state of perfection, although inward perfection is required in order that one exercise such acts worthily.
In like manner, neither are they placed in the state of perfection on the part of the cure which they take upon themselves. For they are not bound by this very fact under the obligation of a perpetual vow to retain the cure of souls; but they can surrender it--either by entering religion, even without their bishop's permission (cf. Decret. xix, qu. 2, can. Duae sunt)--or again an archdeacon may with his bishop's permission resign his arch-deaconry or parish, and accept a simple prebend without cure, which would be nowise lawful, if he were in the state of perfection; for "no man putting his hand to the plough and looking back is fit for the kingdom of God" (Luke 9:62). On the other hand bishops, since they are in the state of perfection, cannot abandon the episcopal cure, save by the authority of the Sovereign Pontiff (to whom alone it belongs also to dispense from perpetual vows), and this for certain causes, as we shall state further on (Q. 185, A. 4). Wherefore it is manifest that not all prelates are in the state of perfection, but only bishops.
Reply Obj. 1: We may speak of priest and bishop in two ways. First, with regard to the name: and thus formerly bishops and priests were not distinct. For bishops are so called "because they watch over others," as Augustine observes (De Civ. Dei xix, 19); while the priests according to the Greek are "elders." [*Referring to the Greek episkopos and presbyteros from which the English 'bishop' and 'priest' are derived.] Hence the Apostle employs the term "priests" in reference to both, when he says (1 Tim. 5:17): "Let the priests that rule well be esteemed worthy of double honor"; and again he uses the term "bishops" in the same way, wherefore addressing the priests of the Church of Ephesus he says (Acts 20:28): "Take heed to yourselves" and "to the whole flock, wherein the Holy Ghost hath placed you bishops, to rule the church of God."