For thousands of years, our ancestors believed in the existence of many Gods. So when they abandoned polytheism and adopted monotheism, did that mean that the old Gods ceased to exist, or that they never existed to begin with?
If the Gods never actually existed, then to be consistent, neither does the one God, either, for it was just a change of BELIEF, and there is no more empirical evidence for the existence of the latter, than for the former.
So if we no longer believe in the GODS, why the belief in GOD?