Why do people deny that God exists, if they can know him by reason?
To know the invisible God is a great challenge for the human mind. Many are scared off by it. Another reason why some do not want to know God is because they would then have to change their life. Anyone who says that the question about God is meaningless because it cannot be answered is making things too easy for himself.
Can we grasp God at all in concepts? Is it possible to speak about him meaningfully?
Although we men are limited and the infinite greatness of God never fits into finite human concepts, we can nevertheless speak rightly about God.
In order to express something about God, we use imperfect images and limited notions. And so everything we say about God is subject to the reservation that our language is not equal to God’s greatness. Therefore we must constantly purify and improve our speech about God.
CCC section (39-49)