XV.  What of that, they will say perhaps; do not the Greeks also believe in one Godhead, as their more advanced philosophers declare?  And with us Humanity is one, namely the entire race; but yet they have many gods, not One, just as there are many men.  But in this case the common nature has a unity which is only conceivable in thought; and the individuals are parted from one another very far indeed, both by time and by dispositions and by power.  For we are not only compound beings, but also contrasted beings, both with one another and with ourselves; nor do we remain entirely the same for a single day, to say nothing of a whole lifetime, but both in body and in soul are in a perpetual state of flow and change.  And perhaps the same may be said of the Angels “Similarly it is clear concerning the Angels, that they have a being incapable of change, so far as pertains to their nature, with a capacity of change as to choice, and of intelligence and affections and places, in their own manner” (S. Thomas Aq., Summa, I., x., 5). and the whole of that superior nature which is second to the Trinity alone; although they are simple in some measure and more fixed in good, owing to their nearness to the highest Good.