One of the things we know about St. Thomas Aquinas is that late in his life he was granted some kind of vision of God. Arising from it, he said that everything he had written was but as straw compared to what he had seen; and he died shortly thereafter, having left his massive Summa Theologiae unfinished.
Sometimes I hear this described as a belated humility on Thomas’ part, a recognition as to how inadequate his understanding of God was. But Thomas’ work was in the tradition of “negative theology”, the via negativa, in which we study God in terms of what we know He isn’t. For example, when we say that God is infinite, we are really saying He has no bounds, no constraints: He is not constrained as we are.
No, I think it was something else.
Consider the work of art that you love most: the painting or the poem or the novel or the piece of music that most moves you. Now, imagine writing down all of the most important things about it. Try to convey exactly why and how it moves you, so that some one else can understand it intellectually. You might be able to do that, if you’re a gifted writer and you truly know your subject.
Now, imagining try to capture it in words so well that someone else will share your experience of it, even without having seen or heard or read the work of art in question. I think you’d find it can’t be done. Your words will always fall short, and the greater the work of art the farther your words will fall short.
And this is what happened to Thomas. Having studied his God for most of his life, and having written about Him about as well and thoroughly as one can, he was granted a glimpse of the Beatific Vision, a glimpse of the glory and beauty that is God. And then he knew how inadequate his work was—not that it was wrong, not that he had written badly, but how little of that glory he had managed to capture, how little of that glory it is possible to capture in mere words.