Neti neti

Do not think that because I call it a ‘darkness’ or a ‘cloud’ it is the sort of cloud you see in the sky, or the kind of darkness you know at home when the light is out. That kind of darkness or cloud you can picture in your mind’s eye in the height of summer, just as in the depth of a winter’s night you can picture a clear and shining light. I do not mean this at all. By ‘darkness’ I mean ‘a lack of knowing’ — just as anything that you do not know or may have forgotten may be said to be ‘dark’ to you, for you cannot see it with your inward eye. For this reason it is called ‘a cloud’, not of the sky, of course, but ‘of unknowing’, a cloud of unknowing between you and your God.

— The Cloud of Unknowing

That which is infinite is known only to itself. This it is which gives some notion of God, while yet beyond all our conceptions — our very incapacity of fully grasping him affords us the idea of what he really is. He is presented to our minds in his transcendent greatness, as at once known and unknown.

— Tertullian