Angels and all beings other than God are made: He only is His own Being. All others exist by created participation; and that which is by participation is caused by that which is by essence. Moses, in his account of Creation, may have omitted all mention of the angels, lest the Israelites should fall into the idolatry to which they were inclined; but all intelligent beings, of whatever substance superior to corporeal nature, are, according to Saint Augustine, comprehended under the title of Light or Heaven. Thus the angels are not eternal, but created by the Will of God, which, though one with His Essence, produces freely without necessity.
Holy men among the Greek Doctors have held that the angels were produced before the creation of the world; but the opinion of the Latins is more probable, namely, that they were created together with corporeal creatures; for they form part of the universe, and a portion is imperfect apart from the whole. Since, then, the angels bear relation to other creatures, and the works of God are perfect, it is probable that they were created at the same time as corporeal substances. It was suitable, moreover, that they should be created in the Empyreal Heavens, as in the highest body; not as though they were dependent upon corporeal substance according to their being or creation, but to manifest their relation to the lower universe over which they preside.
- text taken from Compendium of the Summa Theologica of Saint Thomas Aquinas, by Bishop Berardus Bongiovanni