If A God exist, why not multiple Gods?

there are three

God the Father

God the Son

God the Holy Ghost

God is the supreme being that was, is, and always will be in exsistence. As such all other things were created by Him and constantly kept in creation by His almoghty power. It is absurd to think that there could be 2 or more infinitely perfect and infinitely powerful beings. By the very definition of Surpreme there can only be one. As for the theory that He has to "fight" to stay that way. That is completely redicoulous. In the Bible, even the demons that hate God with all their being instantly obey the command of Jesus. Again as I said, we know from revelation that He created all things and could just as easily erase all that He created in an instant so He wouldn't have to "fight". Another thing I want to mention is that I saw in the other answers that the Bible "proves" that there is more than one God, I don't know what Bible you are reading but I think I know where your confusion may lie. The Bible does say "God of Israel" and "You shall have no other gods before Me" and such. The first statement may lead you to believe that God is just a tribal God which is false. God chose the Israelites to be His special people to carry on His message of a Messiah because not everyone would be capable of doing such a task because sin had entered the world and although the Israelites were no without sin, they strove to be morally better than everyone else. The second statement is a commandment given by God to His people. He was not telling the Israelites that there were indeed other gods that really existed but He meant that because He is the Surpreme being nothing should be made more important than Him such as money or the golden calf. Also recall the story of Elijiah and the prophets of baal. He called forth hundreds of Baal worshipers and challenged them to set fire to wood they could not... Elijiah soaked wood with water and when he asked The Lord to set fire to the wood it was instantly set ablaze.

Well what do you mean by God? if you mean some powerful being that exists in another dimension somewhere, then of course there might be other beings out there just as there might be other universe. But not all religious traditions believe in a deity. The Eastern Orthodox Christian church does not believe in any god or gods. We believe in the eternal, that which is being itself. Or to quote st. Pual "That in whom all things live move and have their being ". God to us is not some being but is reality itself apart from which nothing exists. Thus there can only be one absolute being one reality.

Of course other divine beings exist. Monotheism is the invention of uninspired philosophers during the Babylonian Exile, not a truth revealed to prophets.

But only one of the gods is our father in Heaven, so we worship only him.

Only one of the lords is our savior and redeemer from sin and from death, so we only follow him.

You want an image of God to serve? Take your pick. There are nine billion of us.

If there were only one God, then there would be no reason to call him Supreme or Most High.

Jesus, St. Paul, and every Jew prior to the Exile were good monolatrists.

An objective reading of the bible indicates that the god of the Jews was just one among many; basically a tribal god. All the things in the old testament about not worshiping other gods does not deny them, it just reinforces that as an Israelite their loyalty must be to the god of Israel.

Religious Monopoly?

There ARE multiple gods. You can make anything into a god. But there is only ONE SUPREME LIVING GOD & that is JEHOVAH. He even tells us to have no other gods before Him because He is a jealous God. So if you go & pray to any other god, you are putting that god before Jehovah God & that is wrong.

There can only be One leader in a country. There can be only One leader in the world. There can be only One leader in the Universe.

What part of "Supreme Being" do you fail to understand?

That would seem a reasonable consideration, but we are not talking about reasonable people.