One use of the word “mystery” doesn’t seem to be much more than a desire to escape the pain of difficult thought – It’s not unheard of for my students to cry “mystery!” with the hope that the class will stop thinking about a theological problem. This desire to escape pain needn’t be mere whining – the pain of thought can be a real insight into the vanity of thinking about a problem. That said, mystery has to mean something more than just a command to stop thinking about something, and mere pain of thought can’t tell us whether we’ve hit something insoluble absolutely or only insoluble given our background assumptions. Mere pain can’t tell us whether we should start over, tweak some knobs, or abandon the enterprise altogether. But a deeper problem is that if mystery is nothing but a sort of command not to think about something (pink elephants?) then the mystery had a more perfect mode of being before it was revealed at all. Our minds are never better able not to think about something than when we are totally oblivious to it. Mystery in this sense would be an argument against revelation. I suppose one could argue that the whole point of the revelation was to reveal insoluble problems so that we would think about them, crash into contradiction, and give up, and so “humble the mind” but this is pedagogy of frustration is simply bad teaching and has no place in God’s activity. Christ never learned or taught anything like this i.e. by sending disciples on wild-goose hunts in the hope that they would humble themselves in the face of the wild goose, or perhaps pine more ardently to catch wild geese in the great hereafter.
A better metaphor for mystery is the singularity, which is a point where laws and rules break down or fail to apply, but which nevertheless has a clear relation to the things falling under the rules and laws. A black hole cannot be just another object satisfying a relativistic equation, but it is nevertheless predicted by it and best explained by it. Relativity simultaneously breaks down in the face of black holes and also serves as a proof for them; it also has the great benefit of showing precisely why black holes are unintelligible. It’s not as if Ptolemaic astronomy could do this.
Even if we took mystery as the unintelligible, unintelligibility still needs some sort of conceptual context. Black holes are unintelligible in both Ptolemaic vs. Relativistic physics, but the unintelligiblity is completely different in both. In the first the black hole is something we are either oblivious to or which is pure fantasy, and it is not something revealed as unknown in the theory itself. There is simply no context at all for such the singularity to show itself.
Divine things always have some level of mystery to them since God simply is the point at which the rules, laws and oppositions of created things break down. Hans Kung was right to notice that the cosmological argument confronts us with a being such that the opposition between being and nothing breaks down, but he was wrong to read this as a critique of cosmological arguments. The ontology of a singularity is not this simple. One would eliminate singularities if he could, but the theory is not critiqued by their presence. This could even be taken as an argument that we cannot rule out the possibility of singularity.
Still, singularity is a necessary but insufficient metaphor for mystery. There are times when we simply seem to lack a relevant premise or insight to decide a problem, and so we’re left only to frame possible solutions. The problem of evil seems to be a case where this happens. Even though I have very little doubt that the problem fails, I have no ability to decide among some number of possible resolutions.