The Works of Dionysius the Areopagite, tr. by John Parker, , at sacred-texts.com
A Repetition and Summary of the Angelic discipline.
We have concluded, then, that the most reverend Order of the Minds around God, ministered by the perfecting illumination through its immediate elevation to it, is purified, and illuminated, and perfected by a gift of light from the Godhead, more hidden and more manifest--more hidden, indeed, as being more intelligible, and more simplifying, and more unifying; more manifest, as being a first gift and a first manifestation, and more complete, and more affused to it as transparent. And from this (Order) again, in due degree, the second, and from the second, the third, and from the third, our Hierarchy, is reverently conducted to the super-original Origin and End of all good order, according to the self-same law of well-ordered regularity, in Divine harmony and proportion.
Now all Angels are interpreters of those above them, the most reverend, indeed, of God, Who moves them, and the rest, in due degree, of those who have been moved by God. For, to such an extent has the superessential harmony of all things provided for the religious order and the regulated conduct of each of the rational and intellectual beings, that each rank of the Hierarchies, has been placed in sacred order, and we observe p. 42 every Hierarchy distributed into first, and middle, and last Powers. But to speak accurately, He distinguished each Division itself, by the same Divine harmonies; wherefore the theologians say that the most Divine Seraphim cry one to another, indicating distinctly, as I think by this, that the first impart their knowledge of divine things to the second.
I might add this not inappropriately, that each heavenly and human mind has within itself its own special first, and middle, and last ranks, and powers, manifested severally in due degree, for the aforesaid particular mystical meanings of the Hierarchical illuminations, according to which, each one participates-, so far as is lawful and attainable to him, in the most spotless purification, the most copious light, the pre-eminent perfection. For there is nothing that is self-perfect, or absolutely without need of perfecting, except the really Self-perfect and preeminently Perfect.