Angels are altogether incorporeal

Aquinas noted: "In corporeal substances rank between God and corporeal creatures" ("Treatise on the Angels"). At minimum this means that angels do not have a corporeal nature such as humans. However, in the larger sense, this teaches us that there is a plethora of beings that stand between humans and God. We are not at the apex of creation. This tends to bring a little humility to the human race. Angels are also a challenge to philosophical materialism. That which is intellectual and spiritual stands above the material. This does not negate the goodness of the material world, as in Gnosticism, but it does bring a sense of ordering and priority to life. As Jesus said, "what profits a man if he gain the whole world and loose his soul."

Angels are created

Augustine wrote (Gen. ad lit.ii): "Since the angels were created, in the eternity of the Word, they enjoy holy and devout contemplation." Or as Aquinas put it, "It must be affirmed that angels and everything existing, except God, were made by God. God alone is His own existence; while in everything else the essence differs from the existence." This means that the angels have no ability to exist without God causing them. Only God is self-existent. Of course, nothing in the entire seen and unseen universe can come into existence without God causing its existence. Even energy/matter itself is totally contingent upon God and cannot exist separate from Him. Therefore, there are no spiritual beings, no matter how exalted they are, that are self-existent except the One and that is God. That is why angels are not divine nor can they ever become divine. No matter how long they may exist, they came into existence by Gods creative action; consequently, they are NOT self-existent. Self-existence means that one is uncreated. Only God is uncreated. The Creator must be uncreated in order for there to be a creation.