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.