James 2:19

People who have faith but not works are like those who merely talk but do not act. They are ones who hold fast to their beliefs. One example of this is those who say that they believe that God is one. What good is a claim to belief in that? James shows the uselessness of this belief by comparing to the demons. You may say that you believe that God is one, but this belief is also shared by the demons. Therefore, faith that God is one doesn't really matter or differentiate you from the demons. Perhaps it is your works that matter based upon the faith that you say that you have.