You should look into logical positivism. It holds that any statement whose truth cannot be determined a priori or a posteriori is meaningless (although it has an issue in that the description of the philosophy itself would fall into the meaningless category). A statmemt like "God exists," as you described, cannot be known through experiment or deductive reasoning. So, the phrase itself is meaningless, as is all religious discussion. Language produces the illusion that "God exists" is a true or false statement by not differentiating between the existence of a dog (pretty obvious) and that of an all powerful, perfect being.

Personally, I dislike logical positivism. It seems like something of a cop-out, but I can see its appeal and utility in some questions. In this instance though, I think the discussion itself has an intrinsic benefit. Even meaningless statements can provide knowledge, if only through linguistic irregularities. That's he entire point behind "Colorless green ideas sleep furiously." It is meaningless, and yet still a valuable part of linguistics discussion. Of course, there that sentence and "God exists" differ some, but I think there is enough overlap for at least some valuable discourse. Also, logical positivism does nothing against prudential arguments like Pascal's Wager, because the statment "It is beneficial to believe God exists" could be determined experimentally (though maybe not yet). So, not all discussion of religion would be meaningless.

Lastly, there's no way you're in my philosophy class, is there? Because you seem to be keeping pace with our discussions surprisingly well.