The first is that of the Angels, the second of the Archangels, the third of the Thrones; and these three orders make the first Hierarchy—not first as to nobility, nor as to creation, for the others are more noble, and all were created together, but first in degree, according to our perception of their exaltation.
Then there are the Dominations; after them the Virtues; then the Principalities; and these make the second Hierarchy.
Above these are the Powers and the Cherubim, and above all are the Seraphim; and these make the third Hierarchy.
And the most potent reason for their contemplation is the number in which the Hierarchies are, and that in which the orders are. For, since the Divine Majesty is in Three Persons, which have one substance, it is possible to contemplate them triply. For it is possible to contemplate the Supreme Power of the Father, which the first Hierarchy gazes upon, namely, that which is first by nobility, and which we enumerate last. And it is possible to contemplate the Supreme Wisdom of the Son; and upon this the second Hierarchy gazes. And it is possible to contemplate the Supreme and most fervent Charity of the Holy Spirit; and upon this the third Hierarchy gazes, which, being nearest to us, gives of the gifts which it receives.
And, since it is possible to regard each person in the Divine Trinity triply, so in each Hierarchy there are three orders which contemplate diversely. It is possible to consider the Father having regard to none but Him; and this is the contemplation of the Seraphim, who see more of the First Cause than any other Angelic Nature. It is possible to consider the Father according as He has relation to the Son, that is, how He is apart from Him, and how united with Him; and this is the contemplation of the Cherubim. It is possible again to consider the Father according as from Him proceeds the Holy Spirit, and how it is apart from Him and how united with Him; and this is the contemplation of the Powers.
And in like way it is possible to contemplate the Son and the Holy Spirit.
Wherefore, there must be nine orders of contemplative Spirits to gaze into the Light, which alone beholds itself completely. And this is not the place to be silent so much as one word. I say, that of all these orders some were lost as soon as they were created, perhaps in number of the tenth part, to restore which Human Nature was created. The numbers, the orders, the Hierarchies, declare the glory of the movable Heavens, which are nine; and the tenth announces this Unity and stability of God. And therefore the Psalmist says: “The Heavens declare the glory of God, and the Firmament showeth His handiwork.” Wherefore it is reasonable to believe that the movers of the Heaven of the Moon are of the order of the Angels, and those of Mercury may be the Archangels, and those of Venus may be the Thrones, in whom the Love of the Holy Spirit being innate, they do their work conformably to it, which means that the revolution of that Heaven is full of Love. The form of the said Heaven takes from this a virtue by whose glow souls here below are kindled to love according to their disposition.