“God is mystery” (CCC 206). In theology we can speak of God in two ways, negatively and analogically.
Negatively we cannot say what God is only what He is not (Of course this doesn’t mean that God is negative). As the creator we cannot say that God is finite as His act of creation is beyond restriction, this means that He must be not-finite or what we can infinite. The consequence of this idea is that we can never actually know what God is, we can only look at creation and say that He is not like it. Or in other words God is mystery!
When we speak about God by analogy, we don’t mean it in the usual sense. What we mean is that God is kind of like X. For example when we say that a dog is good we mean ‘good’ in a different way to if we said that Europe is good. This means when we say that God is good it is meant in a different but not unrelated way. This also means that we cannot know God exactly, and therefore He is mysterious to us.
Just because God is mysterious doesn’t mean we cannot know something about him as both ways of speaking about God should show. I will never fully understand the universe, but I can know something about it, maybe even a lot about it. God is a bit like this, I will never comprehend Him, but I can know something about Him.
“God is mystery” (CCC 206)
We are finite, limited. God is infinite, therefore we can never fully understand God. God will always be a mystery, but a mystery we can know something about.