Nothing will acquaint you better with the incomprehensibility of the Triune God than teaching a class on the Trinity to 6th-grade confirmands. Trying to explain to middle schoolers that God is both 1 and 3, though in different ways, is just as difficult as explaining the same truth to adults. The only difference, I think, is that adults have spent enough time intellectually banging their head against the wall trying to understand the Trinity that they’re fine with settling for the mystery.
The doctrine of the Trinity is probably one of the best examples I can think of to illustrate the historic Christian concept of Divine Incomprehensibility. Divine Incomprehensibility is a phrase the church has used throughout its history as a shorthand for, “We can know things about God, and those things we can know are certainly true. However, we cannot know everything about God; our knowledge of Him cannot be exhaustive.” Hence the word “comprehensible” with the negative prefix “in-“. We cannot comprehend God.
Herman Bavinck, an immensely helpful guide in the matters of God, probably doesn’t go too far when he says, "This theory of the incomprehensibility of God and of the unknowability of his essence also became the starting point and fundamental idea of Christian theology.” It’s important to note that when Bavinck says that God’s essence is unknowable, he doesn’t mean that God isn’t knowable in any meaningful or true sense. What he means is simply that God, in Himself and within the Trinitarian divine life, is unknowable completely. This is the case because there is such a big gap between Creator and creature even before sin enters the picture in Genesis 3.
Bavinck goes on to say this:
He cannot fully impart himself to creatures. For that to be possible they themselves would have to be divine. There is, therefore, no exhaustive knowledge of God. There is no name that makes his essence known to us. There is no concept that fully encompasses him. There is no description that fully defines him. That which lies behind revelation is completely unknowable. We cannot approach it either by our thought, our imagination, or our language.
I’ve spent the past few days in utter thankfulness that God is different than I am. God never has to recharge, He never has to go to sleep, He never gets tired. Divine Incomprehensibility is yet another example of this. What Divine Incomprehensibility means is that God is powerful enough and able enough to keep His promises to us. In fact, it means that He always will, for divine promises are not like human ones. Divine Incomprehensibility means, ultimately, that we will never run out of reasons to worship God.