Here we must take account of one of St. Thomas's conceptual distinctions, which at first seems like unnecessary caviling. It is the distinction between "uncreated" and "created" happiness. We have here something which, while not at all obvious, is nevertheless fraught with consequences for our whole feeling about life. Namely, this: what does indeed make us happy is the infinite and uncreated richness of God; but participation in this, happiness itself, is entirely a "creatural" reality governed from within by our humanity; it is not something that descends overwhelmingly upon us from outside. That is, it is not only something that happens to us; we ourselves are intensely active participants in our own happiness. Beatitude - Thomas is saying - cannot possibly be conceived as a merely objective condition of sheer existence. It is not a mere quality, not pure passivity, not simply a feeling. It is something that takes place in the alert core of the mind... Happiness is an act and an activity of the soul.
Josef Pieper, Happiness and Contemplation
activity, aquinas, beatitude, god, happiness, st-thomas