Some people throughout history worshiped several gods all at once. Others denied the existence of God altogether. Is there a God? Or are there gods? Could there even be more than one God?
Consider everything and suppose that everything consists of every thing that exists and does not exist or is yet to exist, every thing that is. One might argue that a thing that does not exist is still a thing and is therefore part of everything.
Now, among everything, some things came to be; the stars, the planets, the beings that we see. Given that those beings are the ones that came to be out of everything, someone must have chosen those beings out of everything to be. Thus there must be at least one God. Now, could there be more than one God?
Again, consider everything. The claim is that there is one such everything. To prove it, suppose there were more than one everything. Each everything would be a thing, and therefore collecting every thing would make one everything.
Now suppose there were more than one God. Given that there is one everything, they would have to share it, otherwise the existence of more than one God is redundant. By sharing everything, each “God” would own and be capable of less than everything, hence contradicting the definition of a God.
Thus, there can’t be more than one God, and given that there must be at least one God, there is one God.