https://youtu.be/FOyK8rSBKsg?si=vVe5G3rIOtrRI9Tk Do we all believe in the same God? No! We do not believe in the same God. If we are believing in the same God, then why are we having different forms of worship? People who believe in the same God should be worshipping God in the same way. There should not be diversity of worship. The fact that we have different mode of worship tells us that we are worshiping different gods.
If we do service to different gods, which then is the true God? There are those which the Bible refers to as those who are not God. Which one of them is the true God? How can I be sure that I am serving the true God? What makes the other gods not true? All of these questions do not have answers. We are not in the position to ascertain whether someone's god is true of not. Or maybe we can actually do. We can know which one is true because the Bible has revealed to us who the true God is.
The true God is the God of the Bible. He is the one who created everything that is existing. He gave us His words so that we can learn His ways. The Bible tells us of his nature. He is the God that formed us after His likeness. Everyone who worships this God can only come through Jesus Christ. Anyone who denies Jesus Christ is not worshiping the true God. Jesus Christ is the way by which we can get to Him.