Thomas Aquinas, Compendium of Theology

The divine goodness is not only the end of the creation of things; it must also be the end of every operation and movement of any creature whatever. The action of every being corresponds to its nature; for example, what is hot, causes heat. But every created thing has, in keeping with its form, some participated likeness to the divine goodness, as we have pointed out. Therefore, too, all actions and movements of every creature are directed to the divine goodness as their end.

Besides, all movements and operations of every being are seen to tend to what is perfect. Perfect signifies what is good, since the perfection of anything is its goodness. Hence every movement and action of anything whatever tend toward good. But all good is a certain imitation of the supreme Good, just as all being is an imitation of the first Being. Therefore the movement and action of all things tend toward assimilation with the divine goodness.

Moreover, if there are many agents arranged in order, the actions and movements of all the agents must be directed to the good of the first agent as to their ultimate end. For lower agents are moved by the higher agent, and every mover moves in the direction of his own end. Consequently the actions and movements of lower agents must tend toward the end of the first agent. Thus in an army the actions of all the subordinate units are directed, in the last instance, to victory, which is the end intended by the commander-in-chief. But we showed above that the first mover and agent is God, and that His end is nothing else than His goodness. Therefore all the actions and movements of all creatures exist on account of the divine goodness, not, of course, in the sense that they are to cause or increase it, but in the sense that they are to acquire it in their own way, by sharing to some extent in a likeness of it.

Created things attain to the divine likeness by their operations in different ways, as they also represent it in different ways conformably to their being. For each of them acts in a manner corresponding to its being. Therefore, as all creatures in common represent the divine goodness to the extent that they exist, so by their actions they all in common attain to the divine likeness in the conservation of their being and in the communication of their being to others. For every creature endeavors, by its activity, first of all to keep itself in perfect being, so far as this is possible. In such endeavor it tends, in its own way, to an imitation of the divine permanence. Secondly, every creature strives, by its activity, to communicate its own perfect being, in its own fashion, to another; and in this it tends toward an imitation of the divine causality.

The rational creature tends, by its activity, toward the divine likeness in a special way that exceeds the capacities of all other creatures, as it also has a nobler existence as compared with other creatures. The existence of other creatures is finite, since it is hemmed in by matter, and so lacks infinity both in act and in potency. But every rational nature has infinity either in act or in potency, according to the way its intellect contains intelligibles. Thus our intellectual nature, considered in its first state, is in potency to its intelligibles; since these are infinite, they have a certain potential infinity. Hence the intellect is the species of species, because it has a species that is not determined to one thing alone, as is the case with a stone, but that has a capacity for all species. But the intellectual nature of God is infinite in act, for prior to every consideration it has within itself the perfection of all being, as was shown above. Accordingly intellectual creatures occupy a middle position between potency and act. By its activity, therefore, the intellectual creature tends toward the divine likeness, not only in the sense that it preserves itself in existence, or that it multiplies its existence, in a way, by communicating it; it also has as its end the possession in act of what by nature it possesses in potency. Consequently the end of the intellectual creature, to be achieved by its activity, is the complete actuation of its intellect by all the intelligibles for which it has a potency. In this respect it will become most like to God.