B. A lost person can attend church regularly. Dead faith means there is no works. To possess faith and not perform works is dead faith. Dead faith will not save you. If our faith in Christ does not activate our soul for service to God in many ways, then James is saying we have dead faith, and we are not saved.
Dead faith brings idle words.
We take prayer requests in every service. In many cases there are life and death situations. If we promise a person to pray for them, and don't, then we have uttered idle words, and there is no profit for anyone in such a thing. Supposing we know of a family in our midst who is having a hard time financially. Maybe the situation is that all we have is just what they need.