God’s essence is unknowable to men, and even to angels.
 Bertrand Russell, A History of Western Philosophy (1945). copy citation

Context

“In the realm of not-being he includes various things, for example, physical objects, which do not belong to the intelligible world, and sin, since it means loss of the divine pattern. That which creates and is not created alone has essential subsistence; it is the essence of all things. God is the beginning, middle, and end of things. God’s essence is unknowable to men, and even to angels. Even to Himself He is, in a sense, unknowable: “God does not know Himself, what He is, because He is not a what; in a certain respect He is incomprehensible to Himself and to every intellect.”* In the being of things God’s being can be seen;” source