Gandalf, the idea of God was not a rational creation of someones mind. It comes from peoples mystical experiences. When they were in such alterated states of consciousness (where reason is usually useless or even meaningless), they percieved that there was a "source" from everything that was and is (and will be), and when returned to "normal" waking consciousness, they called it "God", and tried to fit it in human concepts, for describing it to others.
But as God is far beyond any human concept, they had a hard time doing it, and the best they could was say that it was everywhere, that it could do anything, that it knew everything, and so... this descriptions being only the best way they could fit the greatness of God in mere human concepts and words. God is beyond words, beyond concepts, beyond anything our human minds can reach.
But people insists in treating it as one concept, as one thing that the human mind can understand. And doing so, obviously they are not talking about the God that Is, but about a human concept that i will call god (without capital letter).
So, IMHO, anybody who never did "see" God, or rather, who never had a mystical experience and percieved Him as He is, simply dont know what they are talking about when talks about God. It includes myself, as i never had such mystical experience (yet). But, from what ive understood about this experiences, im sure that my explanation will make sense to the ones who actually had such experiences, and who are the only rightly entitled to talk about God.