Celestial Hierarchies - Chapter X
Recapitulation and summary of the Angelic Hierarchies.
...Each Order is the interpreter and herald of those above it, the most venerable being the interpreter of God who inspires them, and the others in turn of those inspired by God. For that super-essential harmony of all things has provided most completely for the holy regulation and the sure guidance of rational and intellectual beings by the establishment of the beautiful choirs of each Hierarchy; and we see that every Hierarchy possesses first, middle and last powers.
But to speak rightly, He also divided each rank in the same divine harmonies, and on this account the Scriptures say that the most divine Seraphim cry one to another, by which, as I think, it is clear that the first impart to the second their knowledge of divine things.
This may fittingly be added, that each Celestial and human intelligence contains in itself its own first, middle and last powers, which are manifested in a way analogous to the aforesaid ordination belonging to each of the Hierarchical illuminations; and accordingly each intelligence, as far as is right and attainable to it, participates in the most spotless purity, the most abundant light, and the most complete perfection...