Chapter 73 — Of the diversity, gradation, and order of things

Moreover, diversity among things was rightly established according to a definite order, so that some things might be more excellent than others. For this pertains to the lavishness of the divine goodness, that God should communicate a likeness of his goodness to created things as far as possible. Now, God is not only good in himself, but exceeds other beings in goodness, and guides them toward goodness. Consequently, so that the likeness which created beings bear to God might be heightened, it was necessary for some things to be made better than others, and for some to act upon others by leading them toward perfection.

Further, the diversity among things consists chiefly in diversity of forms. Formal diversity is achieved by way of contrariety; for a genus is divided into various species by contrary differences. But order is necessarily found in contrariety, for of two contraries one is always better than the other. Therefore, diversity among things had to be established by God with a particular order, such that some beings are more excellent than others.