“The Whole Universe Together” and the Diversity of Creatures.
According to St. Thomas Aquinas, God created the diversity of creatures because no single creature can adequately reflect the perfection of God:
“We must say that the distinction and multitude of things come from the intention of the first agent, who is God.
For He brought things into being in order that His goodness might be communicated to creatures, and be represented by them; and because His goodness could not be adequately represented by one creature alone, He produced many and diverse creatures, that what was wanting to one in the representation of the divine goodness might be supplied by another.
For goodness, which in God is simple and uniform, in creatures is manifold and divided and hence the whole universe together participates in the divine goodness more perfectly, and represents it better than any single creature whatever.” (Summa theologiae, I.47.1)