Deuteronomy 4:39 Know therefore this day, and consider it in thine heart, that the LORD he is God in heaven above, and upon the earth beneath: there is none else.
The people of Israel needed to stop and think on this very day. We need to do this daily. Think about this. God in heaven is the only God. There are no other gods. We do not serve the Christian god while others serve their gods. There is not a god of Israel and different god for other countries. There is only one God, and He is the God of the Bible.
You need to know this in your heart of hearts. You need to realize that we are talking about the only God. Now have you believed in Him. Have you trusted Him with your salvation? If not, then you are in rebellion against the only God of the universe. Have you trusted Him? Are you obeying him? Then you are worshipping and serving the only true God.