God is neither a made-up concept, nor the universe. God is instead, something deeper than both, and none. In short, God is the quintessential mystery. How can it be so? From this perspective, the universe itself is a sacred object, not just an aggregate of ideas. Something entirely other is here. This is a different vantage point than the one we perceive through our experience of it.
The universe is a vehicle, a simple machine that serves our purposes, rather than a conceptual explanation for what happens around us. Perhaps God, in that perspective, is not a concept at all, but an experience. One where you discover a light in the dark, not something you saw, but something you felt. In this view, God is not a reductionist collection of mental objects. Rather, God is all there is, and all there could be, and all there is yet to be. Now you understand why God is a mystery, and not a concept.