“What is the problem of the natural desire or desiderium naturale? Fundamentally it is the paradox of a natural desire for a supernatural end. The problem therefore arises from a certain tension within the Thomistic synthesis. On the one hand, Aquinas aims to show along Aristotelian lines that beatitude is found in the possession of a self-sufficient good which fulfills and perfects the inclinations immanent within human nature itself. On the other hand, he wishes to maintain the doctrine affirmed in sacred scripture that salvation is God’s free and unmerited gift made efficacious through the cross and resurrection of Jesus Christ.
“For Aquinas to integrate the two positions he had to show that on the one hand, the vision of the Divine essence to which man is ordained corresponds to an immanent human desire, and, on the other hand, that the fulfillment of this desire wholly transcends the natural power of man to attain. Aquinas does this by casting the vision of God as the fulfillment of the intellect’s orientation to quiddity or essences. By nature the intellect desires to know things according to their essence (their whatness) and is not satisfied merely to know their existence (their thatness). Since, according to his natural theology, it is possible for man by natural reason to know of the existence of the First Cause, if it did not arrive at knowledge of the essence of the First Cause there would remain in the intellect a natural desire to know the essence of the First cause. But says Aquinas such quiddiative knowledge of God transcends the natural power of the human intellect.”