I think whoscarl is probably right. God is likely a (natural) creation of our minds. Worship of God can bring about physical and mental changes akin to those of drugs. Quite simply, God is addictive - its spiritually uplifiting, it makes people feel secure and meaningful - gives life purpose (also gives insights into the infinite, the 'beyond.')

Unfortunately it also drives people to kill each other, start wars, and force their beliefs upon 'primitive' peoples.