Some nuggets from Thomas.
The first from his commentary on the Sentences (XLIV, 1, 2): “They reason falsely [who say that] since an angel is better than a stone, therefore two angels are better than one angel and a stone . . . . Although an angel, considered absolutely is better than a stone, yet two natures are better than one only; and therefore a universe containing angels and other things is better than one containing angels only; since the perfection of the universe is attained essentially in proportion to the diversity of natures in it, whereby the diverse grades of goodness are filled, and not in proportion to the multiplication of individuals of a single nature.”
The second from Summa Contra Gentiles : “A thing approaches to God’s likeness the more perfectly as it resembles Him in more things. Now, goodness is in God, and the outpouring of goodness into other things. Hence, the creature approaches more perfectly to God’s likeness if it is not only good, but can also act for the good of other things, than if it were good only in itself; that which both shines and casts light is more like the sun than that which only shines. But no creature could act for the benefit of another creature unless plurality and inequality existed in created things. For the agent is distinct from the patient and superior to it. In order that there might be in created things a perfect representation of God, the existence of diverse grades among them was therefore necessary.”
Headline: Thomas Affirms Difference!