I believe it is a matter of faith that God exists!
I happen to believe that us Jews and Christians believe there is only one. Furthermore, Islam also believes in one God. Whether we all agree is another question.
However, when one looks at the order, beauty, complexity, and nature of the physical world, it is clear that one being or many beings put this altogether.
Furthermore, when one looks at all of the moral chaos and natural disasters, one might even consider that some of the gods are evil.
I think history is replete with examples of this.