But someone will say, “You have faith and I have works.” Show me your faith apart from your works, and I will show you my faith by my works. You believe that God is one; you do well. Even the demons believe—and shudder!… For as the body apart from the spirit is dead, so also faith apart from works is dead. (JAS 2:18-19, 26 ESV)
We often say that if you want to become a Christian that you must believe in Jesus. Paul writes that if you believe in your heart that Jesus is Lord and confess with your mouth that God raised him from the dead you will be saved.
But what does that mean? This kind of belief is the means through which God changes a person. Real faith manifests itself in a different life. Faith lead to action. Faith that makes no difference in the choices you make or the goals you set is no different from that of the demons. It is not saving faith.
So whoever knows the right thing to do and fails to do it, for him it is sin. (JAS 4:17 ESV)
And it isn’t just saying no, to what God says not to do, it is saying yes to what God says we are to do.