Christian theology moves between two poles. On the one hand, it is impelled by the desire to understand God. Understanding implies explanation, and explanation is essentially a matter of giving reasons. This impulse leads us to ask why God is or does thus or so. If we cannot find clear reasons, then we at least seek for careful definitions. We may not be able to say why God is Triune, but we at least attempt to formulate as precisely as we can what the Trinity means. This theological pole could be called the rational impulse in theology.
At the other pole, theologians constantly bump up against the recognition that God is wholly other. They quickly learn that the predicates that we apply to God cannot be used univocally. Even so basic an assertion as “God exists” has to mean something different than the assertion that “we exist,” for God’s being is underived. He alone is self-existent—His being is different than our being.
Faced with the limitations of human understanding and human language, theologians sometimes despair of any rational knowledge of God. For them, theology becomes purely a matter of negation. They cannot meaningfully say what God is. They can only say what He is not. Rational knowledge of God is impossible.