Do We Know What God is ‘Really’ Like?
The defining qualities of God are the qualities that make him God, that distinguish him from all other beings. If we are going to use the word essence, it is best to understand it is comprising all the divine attributes revealed in Scripture. That God has many defined features does not compromise his simplicity, if we maintain that those attributes are inseparably one in God. But then we can state what his essence is, and we can do it in many ways: control, authority, presence, holiness, eternity, goodness, and so on.
Is God’s essence, then, knowable? Yes and no. Yes, in that Scripture tells us about some qualities that define God as distinct from other beings… And when Scripture describes God, it describes him as he really and truly is. So it’s definitions of God enable us to know him, indeed, to know his essence.
No, God’s essence is not knowable, in that our knowledge of God is certainly not exhaustive. We don’t know everything that came to be known about God’s holiness, wisdom, goodness, etc., nor how all his attributes are unified within the complete divine being. To have a perfect knowledge of that, we would have to be God. Such knowledge is impossible for the creature. The best formulation, then, is that God’s essence is knowable, but not exhaustively.
We should not adopt a mental picture or model of God in which his real identity or essence is hidden in darkness, while his revealed nature is a kind of periphery around that darkness. In that picture, the darkness conceals what God really and truly is; his revealed nature is something less than his real being. On the contrary: God’s names and revealed attributes tell us what he truly is, at the heart of his being. There is nothing more fundamental about him that could call his revealed nature into question. Such biblical terms as holiness, goodness, and eternity express God’s essence. They tell us what he really is, for Scripture is true. They define him, because through them God has defined himself.
-John M. Frame, The Doctrine of God, 204-205