If Hierarchy, which signifies sacred principality, be considered on the part of its Chief, all angels and rational creatures form one sole hierarchy, because there is one Head over all, namely, God; but if it be considered on the part of the angels, there are three hierarchies.
For, with regard to any multitude governed, unity is understood to signify that the rule of the chief is received after a single mode; but angels and men are governed by different modes; the former by pure illuminations, the latter by sensible similitudes.
The angels likewise form different hierarchies, because the superior angels, illuminated by more universal conceptions which come directly from God, have a mode of understanding different from that of inferior ones; therefore they form different hierarchies. Angels of the intermediate class are so illuminated that their conceptions, depending on universal created causes, are multiple and divided; while the inferior ones derive theirs from individual objects, as these depend upon immediate causes. But those are in error who admit hierarchy in the Divinity, where there exists no Order except that of Nature only.
Every hierarchy must comprise different Orders, without which there would be a confused multitude. Hence diversity of order is essential to the idea of hierarchy. These Orders are to be considered as bearing reference to their respective actions and offices, but they may all be reduced to three; for every perfect multitude has a beginning, a middle, and an end; as in a city we find three Orders of men, viz. the aristocracy, the middle class, and the populace.
Angels have all things in common, nevertheless one possesses more perfectly than another. Moreover, as far as our knowledge goes, there are many angels in each Order; for owing to our very imperfect knowledge we can speak of their collective Orders only, which comprise many. A more perfect knowledge would enable us to distinguish their various offices; for as every star has its order and use, so every angel.
The distinctions of Order, as these refer to their supernatural end, are, in the case of the angels, the gift of grace as the complement of nature. In men they are by grace alone; for gifts of grace are not given to men in proportion to their natural gifts, while among the angels such gifts are proportioned to their natural capacity. Thus spiritual perfections, although common to all, abound more in the superior than in the inferior. For in every Order the same thing may be said to exist in one of three ways, viz. properly, when it is proportioned to the nature of the subject; as reason is attributed to the man; by excess, when the thing attributed is less than that to which it belongs, as that in respect of the sun, or the perfections of creatures ascribed to God; or by participation, when that which is attributed is not found fully, but only partially: thus holy men are sometimes called gods. Hence Dionysius explains the names of the different Orders by reference to their spiritual perfections; while Gregory chiefly regards their exterior ministry.
Thus angels bear the less and archangels the more important messages; Virtues work miracles. Powers repel evil spirits, and Principalities direct good spirits.
The rank of the Hierarchies and Orders is likewise suitably distinguished inasmuch as the first Hierarchy is said to know the nature of things in God; the second in universal created causes, and the third in causes as applied to particular effects. The first comprises the Thrones, so exalted as to receive God in themselves and to apprehend conceptions in Him; the Cherubim, who know Divine secrets in a super-eminent manner; and the Seraphim, who excel in union with God.
The second Hierarchy is constituted for government; thus universal rule over action is assigned to the Dominations; over faculties to the Virtues, while the Powers keep order so that precepts may be fulfilled.
The third consists of the executive. These may possess incipient action, as leaders of others, like the Principalities, or they may be simply active, like the angels; while the archangels are between the two.
The angelic Hierarchies will remain after the Day of Judgment as regards their distinctions of rank, which depend upon differences of nature and grace. For these cannot be taken away from them, since natural qualities are only lost by corruption, and degrees of glory will always be in proportion to preceding merit. But their offices will only remain according to the requirements of the future Dispensation: thus they will cease in what concerns bringing others to their final end.
And some men will be assumed into the ranks of the angels; others into higher ranks, according to their gifts of grace and their own merits, not according to their natural gifts; and the society of men and angels will be one, inasmuch as the Beatitude of all consists in union with one God.
- text taken from Compendium of the Summa Theologica of Saint Thomas Aquinas, by Bishop Berardus Bongiovanni