I believe in God because it is a common belief between many races. The people are so varied in their culture it seems unusual that so many would agree on the existence of God and disagree on most everything else once you subtract things required for the survival of the individual or species (eat, drink sex, ect).
People said a long time ago "an apple a day keeps the doctor away" before there was even any proof. It may be just a matter of time until God is proven to exist. Also God can be in any form, because all the different religions describe God differently. They may all be correct. We may just not be capable of understanding God at this time. God could be the undiscovered ether, the substance that quarks and electrons may be composed of. That would make God everywhere, invisible and quite powerful. It also would require faith, because the ether can not be directly observed or measured (there is still a debate as to whether it exists).