Contemporary English Version (CEV)
Here, James illustrates the difference between knowledge and faith. Knowledge means that you are not ignorant of something, that you possess an idea of it, but it may not change anything that you do. It's like when I know that it's cold outside and still don't wear a jacket. My knowledge of the weather doesn't translate into actions, because I don't believe the cold will bother me, or I don't believe it's really that cold outside. Later on, I often realize how unwise it is not to put my knowledge into action.
So James is calling Christians to pay attention and not get caught in the same trap. Our knowledge of Christ and his resurrection should lead to transformation in our lives -- we should be different because of our faith in the risen Christ. The way we treat one another should be transformed by the power of Christ working in and through us. Since Christ selflessly died for us, we should be willing to selflessly serve others.