There is obviously a boundary on human knowledge. The finitude of our being requires a boundary on what we can understand, or boundaries. That boundary is a very important one.
We can, for instance, understand God, but not altogether. We can apprehend God truly, but we never comprehend—to use an old expression. We speak things about God that are true, but we place on him no definition; in fact, we understand him to be altogether unbounded. God is without temporal boundaries, God is without spatial boundaries, God is without ontological boundaries—he is infinite in his being, he is absolute being and the ground of being, nothing exists which does not participate in his being, deriving from him that which it is.
All that is not-God has boundaries. Even the universe, which seems from our perspective infinite, is only a gesture of true infinity; it has its bounds. The category of that which is limited is creation, since all that is not-God is created. God makes boundaries, and limited beings are creatures to whom he says: thus far and no further.
God makes limited things. He puts boundaries on real objects, and these exist because they participate in something of God but not everything. The limits that creatures have also mark the boundaries that represent potential. It is only when you have limits that you have potential, and this is also why we affirm that God is pure actuality.
God is pure actuality because there is no perfection God is lacking. There are many perfections we lack. All creation is a lack of the kind of perfection God enjoys, though it is nevertheless good. Everything in its own way manifests something of God by participating in a limited way in God, and in that way it manifests something about him, and that is its good.
There are things that go beyond our understanding, and God is the chief one because he goes beyond in every way. There is a place at which our limits make the understanding we can have of something fade from our cognitive grasp.
What I am really concerned with here is the manner of that fading. There is a fading of fear, of something that is overwhelmingly terrible, amazingly so and beyond our comprehension. We sense there is more of the awfulness we are aware of existing in ways we cannot comprehend. But there are things that also fade out as they transcend our comprehension that beckon, not with dread, but with desire and amazement. This is wonder.
And it is God who excites both.