Reference to God’s incomprehensible essence also warns us against imagining what God is like, which would lead us inexorably down the road to idolatry. Recognizing God’s infinite and spiritual essence keeps us from thinking that God can be represented in imagery.

Paul Helm, John Calvin’s Ideas (Oxford, 2004), 20.

Here Paul Helm touches on Calvin’s view that the essence of God cannot be understood by the human mind. We can know about God all that he reveals about himself in his Word, but we can’t know more than that. As Helm notes later, the activities of God, which can be known, should not be confused with the essence of God, which cannot be known by the human mind. I often use the illustration (flawed, I know) that God is like Windows 7 and the human mind is like a calculator. A calculator simply does not have the capacity to run Windows 7. Likewise, we do not have the cognitive faculties to comprehend the essence of God, no matter how hard we try.

Calvin warned against philosophical speculation about the essence of God that goes beyond what Scripture has revealed:

Here, indeed, if anywhere in the secret mysteries of Scripture, we ought to play the philosopher soberly and with great moderation; let us use caution that neither our thoughts nor our speech go beyond the limits to which the Word of God itself extends. For how can the human mind measure off the measureless essence of God according to its own little measure, a mind as yet unable to establish for certain the nature of the sun’s body, though men’s eyes daily gaze upon it? Indeed, how can the mind by its own leading come to search out God’s essence when it cannot even get to its own? Let us then willingly leave to God the knowledge of himself. For, as Hilary says, he is the one fit witness to himself, and is not known except through himself. But we shall be “leaving it to him” if we conceive him to be as he reveals himself to us (Institutes 1.13.21).

What does this mean for us? We should worship God as he has revealed himself in Scripture, and not try to understand things for which we were never made (Deut. 29:29)!