I started reading Peter Kreeft’s A Shorter Summa and I understood St. Thomas’ argument for why revelation, not just reason, is necessary for salvation. But why is it that reason cannot fully comprehend God? – Michael Foster
Thomas teaches that in this life we cannot know what God is but only what he is not. This does not mean we cannot know anything about God, but that what we can know can only be known by negation and analogy (I’ll explain those two things in a minute). Why is this the case? Because we only know God through his effects (creation) which in no way match their cause. So, if we can’t know God in this life can we say anything about Him? Aquinas says yes. In fact, he says that it would be contrary to Divine Goodness should God not have revealed something of himself to us. This brings us to what I mentioned a moment ago, negation and analogy. While God’s effects do not match their cause, they do resemble Him. We can look at the perfections of creatures and conclude that these perfections must exist in God in a preeminent way. Wisdom is a perfection, it therefore must exist in God analogously (as opposed to univocally since, again, God is infinite. He is also simple, says Thomas, so while you or I may have wisdom to some degree. God is wisdom). The same can be said with other perfections, such as goodness, love, strength, etc. We can also know about God negatively since he transcends all categories (he cannot be categorized because his essence is existence. It isn’t limited by a particular essence). So we throw off any deficiencies or limits that we see in creatures. So when we say God is omnipotent, omniscient, or omnibenevolent, we are in a sense saying something negative about God. God is not ignorant. God is not ignorant. God is not evil, etc. And since every negation rests on an affirmation (if you say God is not ignorant you have to know what knowledge means), we can know something about God.
Now, while we cannot know God in this life we can know him in the next. But to know God is not the same as comprehending him. Even the blessed in heaven will never comprehend God since you can’t comprehend (literally, bring together) in our minds what is infinite.
I hope that’s a help. I’ll leave you with the respondio from the the first article from Question twelve in the Prima Pars. The article title is, “Whether any created intellect can see the essence of God?” Aquinas answers:
Since everything is knowable according as it is actual, God, Who is pure act without any admixture of potentiality, is in Himself supremely knowable. But what is supremely knowable in itself, may not be knowable to a particular intellect, on account of the excess of the intelligible object above the intellect; as, for example, the sun, which is supremely visible, cannot be seen by the bat by reason of its excess of light.
Therefore some who considered this, held that no created intellect can see the essence of God. This opinion, however, is not tenable. For as the ultimate beatitude of man consists in the use of his highest function, which is the operation of his intellect; if we suppose that the created intellect could never see God, it would either never attain to beatitude, or its beatitude would consist in something else beside God; which is opposed to faith. For the ultimate perfection of the rational creature is to be found in that which is the principle of its being; since a thing is perfect so far as it attains to its principle. Further the same opinion is also against reason. For there resides in every man a natural desire to know the cause of any effect which he sees; and thence arises wonder in men. But if the intellect of the rational creature could not reach so far as to the first cause of things, the natural desire would remain void.
Hence it must be absolutely granted that the blessed see the essence of God.
Read more here.
Matt Fradd speaks to tens of thousands of people every year. He is the best-selling author of several books, including Does God Exist?: A Socratic Dialog on the Five Ways of Thomas Aquinas and The Porn Myth: Exposing the Reality Behind the Fantasy of Pornography. Matt earned his master’s and undergraduate degree’s in philosophy from Holy Apostles College. His podcasts, Love People Use Things and Pints With Aquinas are listened to by tens of thousands of people every month. Matt lives with his wife, Cameron, and their children in Georgia.