There Bible is our book of doctrines in the church of God. We follow the complete doctrines of the church of God as those who follow the true God. There is no other way in which we can serve God without following the doctrines of Jesus Christ.
So, if we are following the doctrines of the church which is what the apostles handed over to us, anyone who does not follow totally what the doctrines which are written in the Bible says is not serving the same God of the church. We have several diversity in doctrines across so many denominations. The differences in doctrines is a clear indication that we are not serving the same God.
There are several organizations in the name of church. Some do not believe in the Lord Jesus Christ. There are also others who do not accept the teachings of the apostle Paul. With all these differences, we cannot deny that fact that we all are serving different gods.