Can We Know God in this Life by Natural Reason?
Our natural knowledge begins from the senses. Therefore our natural knowledge can only extend as far as it can be led by the objects of the senses. On the basis of sensory objects our intellect can not go so far as to see the essence of God, because sensory creatures are effects of God which are not equal in power to their cause. Hence we cannot know the full power of God on the basis of the objects of the senses and consequently we cannot see his essence. However because they are effects that are dependent on a cause, we can be led from them to know that God exists, and to know the characteristics that he must possess as the first cause of all things that transcends everything caused by him. Hence we know about his relationship to his creatures that he is the cause of all, and that creatures differ from him in that he is not a part of the things that he has caused, and that they are separate from him not because of any deficiency on his part but because of his transcendence…
Do We Know God Better through Grace than through Natural Reason?
We have a more perfect knowledge of God through grace than through natural reason. This is true for the following reason: The knowledge we have by natural reason requires two things, images derived from the objects of the senses and the natural light of the intellect which enables us to abstract intelligible concepts from them. In both these operations human knowledge is assisted by the revelation of grace. The natural light of the intellect is strengthened by the infusion of the light of grace, and by the action of God images are sometimes placed in the imaginations of men that better express divine things than those which we naturally receive from the senses … Although by the revelation of grace in this life we do not know what God is and so are joined to him as to one who is not known, we still know him more fully because many of his most excellent works are demonstrated to us, and because through divine grace we attribute to him many things that the natural reason cannot attain—as, for example, that God is three and one.