"Nor in the sense that we understand ‘spirit’ is God spirit; there is no sonship or fatherhood, nor anything else that is known by us or by anyone else. He is none of the things that have no being, none of the things that have being. None of the things that are known know him for what he is. Nor does he know the things that exist for what they are in themselves, but only for what they are in him. Nor is there any way by which we can reach him through reason or understanding: he has no name, we cannot know him; he is neither darkness nor light, error or truth. Speaking generally there is no affirmation we can make of him, nothing we can deny of him."
Dionysius’ Mystical Teaching, published in The Cloud of Unknowing
(Now then, the Christian koan: "Who do you say that I am?" - or maybe, 'What' do you say that I am?)