St. Gregory the Theologian, Oration 38, Section 9:
Yet it was not sufficient for goodness to be moved only in contemplation of itself, but it was necessary that the good be poured forth and spread outward, so that there would be more recipients of its benevolent activity, for this was the summit of goodness. Therefore it first thought of the angelic and heavenly powers, and the thought was action, accomplished by the Word and perfected by the Spirit. And thus were created the second radiances, the servants of the first Radiance, which are either intelligent spirits, or a kind of immaterial and bodiless fire, or some other nature as close to those just mentioned possible. I would like to say that they are unmoved toward evil and have only the movement toward the good, since they are around God and are the first to be illumined by God; for things here below are illumined second. Yet I am persuaded to consider and say that they are not immovable but only difficult to move on account of the one who was called Lucifer because of his radiance but both become and is called darkness because of his pride and the rebellious powers under him, who are fashioners evil through their flight from the good and incite evil in us.