God, as a word, is open to interpretation and redefining. No religion owns the patent to that word. I actually like the word myself but can see how others don't due to the attempt of many religions to own, control and define it, often in ugly, self-serving ways.
How we define the source of all things (if we believe in such a source, or think such a source necessary) is important in how we choose to understand life and live it. Although this essence that we call source or God is to a large extent unknown it doesn't make it unknowable. If it were then there would be little point talking about it and all the monks in the world (with the exception of the Buddhists) would be wasting their time!
Of course, from the materialistic viewpoint all this is meaningless because even if an entity did somehow give birth to the universe that entity must remain separate from us and therefore unknowable. From such a view talk of a cosmic source remains an unsubstantiatable flight of fancy!
Only from the idealist viewpoint does the idea of a God or source of being that we can communicate with make any sense. If the universe is mind outpictured as matter then God/Source becomes relevant, otherwise it is just a word, like the spaghetti monster, that people can endlessly, emptily, debate!