Whether the Angels that Fell Partook of the Blessedness Which the Holy Angels Have Always Enjoyed from the Time of Their Creation
And since these things are so, those spirits whom we call angels were never at any time or in any way darkness, but, as soon as they were made, were made light; yet they were not so created in order that they might exist and live in any way whatever, but were enlightened that they might live wisely and blessedly. Some of them, having turned away from this light, have not won this wise and blessed life, which is certainly eternal, and accompanied with the sure confidence of its eternity; but they have still the life of reason, though darkened with folly, and this they cannot lose even if they would.
But who can determine to what extent they were partakers of that wisdom before they fell? And how shall we say that they participated in it equally with those who through it are truly and fully blessed, resting in a true certainty of eternal felicity? For if they had equally participated in this true knowledge, then the evil angels would have remained eternally blessed equally with the good, because they were equally expectant of it. For, though a life be never so long, it cannot be truly called eternal if it is destined to have an end; for it is called life inasmuch as it is lived, but eternal because it has no end.
Wherefore, although everything eternal is not therefore blessed (for hell-fire is eternal), yet if no life can be truly and perfectly blessed except it be eternal, the life of these angels was not blessed, for it was doomed to end, and therefore not eternal, whether they knew it or not. In the one case fear, in the other ignorance, prevented them from being blessed. And even if their ignorance was not so great as to breed in them a wholly false expectation, but left them wavering in uncertainty whether their good would be eternal or would some time terminate, this very doubt concerning so grand a destiny was incompatible with the plenitude of blessedness which we believe the holy angels enjoyed.
For we do not so narrow and restrict the application of the term “blessedness” as to apply it to God only, though doubtless He is so truly blessed that greater blessedness cannot be; and, in comparison of His blessedness, what is that of the angels, though, according to their capacity, they be perfectly blessed?
Source: City of God (New Advent)