All creatures, in their own way, seek to imitate the divine likeness. Man, though, does this in a way that is absolutely unique. Material substances, as material, are characterized by a certain finitude that is absent in creatures who possess an immaterial principle. Man’s immaterial principle, the soul, possesses an intellect which is in potency to intelligible species. In other words, the intellect is able to receive the forms of other substances without itself being determined to one thing. Potentially, the intellect of man is infinite.
The intellect of God is actually infinite. He essentially contains the perfections of all beings in a pre-eminent way (as was shown in a previous post). By fulfilling its potential for possessing all that is intelligible, then, man becomes more like God than any other creature.
Man’s knowing power begins with sensation. Our intellectual activity consists in rendering actually intelligible that which is only potentially intelligible within the objects of sensation. The end of man, then, cannot be fulfilled in this way. Man’s natural power of knowledge is proportioned to sensible objects, but he desires perfect knowledge of all that is, which means that he must acquire knowledge of that which cannot be sensed, i.e. immaterial substances.