The Works of Dionysius the Areopagite, tr. by John Parker, , at sacred-texts.com
Why the Hierarchs amongst men are called Angels.
But this is sometimes also asked by diligent contemplators of the intelligible Oracles; Inasmuch as the lowest Orders do not possess the completeness of the superior, for what reason is our Hierarch named by the Oracles, "Angel of the Sovereign Lord?"
Now the statement, as I think, is not contrary to what has been before defined; for we say that the last lack the complete and pre-eminent Power of the more reverend Divisions; for they participate in the partial and analogous, according to the one harmonious and binding fellowship of all things. For example, the rank of the holy Cherubim participates in higher wisdom and knowledge, but the Divisions of the Beings beneath them, participate, they also, in wisdom and knowledge, but nevertheless partially, as compared with them, and p. 45 in a lower degree. For the participation of wisdom and knowledge throughout is common to all the minds which bear the image of God; but the being near and first, or second and inferior, is not common, but, as has been determined for each in its own degree. This also one might safely define respecting all the Divine Minds; for, as the first possess abundantly the saintly characteristics of the inferior, so the last possess those of the superior, not indeed in the same degree, but subordinately. There is, then, as I think, nothing absurd, if the Word of God calls our Hierarch, Angel, since he participates, according to his own capacity, in the messenger characteristic of the Angels, and elevates himself, as far as attainable to men, to the likeness of their revealing office.
But you will find that the Word of God calls gods, both the Heavenly Beings above us, and the most beloved of God, and holy men amongst us, although the Divine Hiddenness is transcendently elevated and established above all, and no created Being can. properly and wholly be said to be like unto It, except those intellectual and rational Beings who are entirely and wholly turned to Its Oneness as far as possible, and who elevate themselves incessantly to Its Divine illuminations, as far as attainable, by their imitation of God, if I may so speak, according to their power, and are deemed worthy of the same divine name. p. 46