Reply Obj. 2: As regards knowing God Himself, Whom all see in one way—that is, in His essence—there is no hierarchical distinction among the angels; but there is such a distinction as regards the types of created things, as above explained.
Reply Obj. 3: All men are of one species, and have one connatural mode of understanding; which is not the case in the angels: and hence the same argument does not apply to both. _______________________
SECOND ARTICLE [I, Q. 108, Art. 2]
Whether There Are Several Orders in One Hierarchy?
Objection 1: It would seem that in the one hierarchy there are not several orders. For when a definition is multiplied, the thing defined is also multiplied. But hierarchy is order, as Dionysius says (Coel. Hier. iii). Therefore, if there are many orders, there is not one hierarchy only, but many.
Obj. 2: Further, different orders are different grades, and grades among spirits are constituted by different spiritual gifts. But among the angels all the spiritual gifts are common to all, for "nothing is possessed individually" (Sent. ii, D, ix). Therefore there are not different orders of angels.
Obj. 3: Further, in the ecclesiastical hierarchy the orders are distinguished according to the actions of "cleansing," "enlightening," and "perfecting." For the order of deacons is "cleansing," the order of priests, is "enlightening," and of bishops "perfecting," as Dionysius says (Eccl. Hier. v). But each of the angels cleanses, enlightens, and perfects. Therefore there is no distinction of orders among the angels.
On the contrary, The Apostle says (Eph. 1:20,21) that "God has set the Man Christ above all principality and power, and virtue, and dominion": which are the various orders of the angels, and some of them belong to one hierarchy, as will be explained (A. 6).
I answer that, As explained above, one hierarchy is one principality—that is, one multitude ordered in one way under the rule of a prince. Now such a multitude would not be ordered, but confused, if there were not in it different orders. So the nature of a hierarchy requires diversity of orders.
This diversity of order arises from the diversity of offices and actions, as appears in one city where there are different orders according to the different actions; for there is one order of those who judge, and another of those who fight, and another of those who labor in the fields, and so forth.