God has said, "I am The Lord your God. You shall have no other gods before me." It is up to every man to make sure that the god who is being worshiped and served is truly God. His word describes His will and His commandments describe His standard of holiness.
Every compromise of God's word becomes the foundation for worshiping a false "god". When God's word is changed to suit the worshipper, they create a "god" in their own image...and a demon is sure to empower it. This is the reason people have such faith in their gods. This is the reason people can come home from their time of worship feeling 'blessed' even though God's word is not preached and His Spirit is not worshiped.
Demons are the 'gods' and they are real and they are powerful and they are convincing. Having a sense of comfort and peace does not indicate that God was present.
Love The Lord God with all your heart, soul, mind and strength. We know Him by His Word. But if a man changes God's Word to accomodate his personal belief system, he makes a god in the image he prefers...and therefore is not worship The Lord God.