We do not serve the same God. Some serve the almighty God while others serve Man-made gods. There are yet others who serve natural things like trees,sun,hills even animals,sea creatures and the rest of them.
God has given man the will power to make choice, so they choose anything to serve accordingly to their convictions and beliefs. I know of a tribe in my own side of the world where people serve Python. They revered it so much that if a python dies, they bury it with the burial rites of a dead king. But there is one mystery i observed, python does not harm anybody from that community even if they come in close contact with it.
The fact that we don't serve the same God was demonstrated at mount Carmel where prophet Elijah and the prophets of Baal engaged in war of supremacy 1Kings 18:20-40. What about the atheists, they do not even believe in the existence of God. And among them are highly educated men and women. So from the ongoing, we do not serve the same God.