James 4:8b

This other thing that is added by James is for them to cleanse their hands and to purify their hearts. He doesn't just tell those who are clean to clean their hands. It wouldn't make sense for you to be asked to clean your room if it's already clean. Instead, he's talking to sinners, telling them to clean their hands. In addition, those who are double-minded are asked to purify their hearts. Instead of wanting both friendship with the world and friendship with God, hopefully they would have hearts only for God.