They'll be free from the enemy because they will exercise authority over him. If you lay hands on the sick then you're exercising authority over the devil. James did not say to pray to God so that He will resist the devil for you. YOU are supposed to resist the devil. Once you exercise it, it will work for you whether you feel it did or not.
Feelings have nothing to do with it.
For we walk by faith, and not by sight. Don't give the devil any place in you. If you give place to the devil, there's nothing Jesus can do because you have the authority and you have given the devil permission to have place in your life. Unless you exercise your authority against the devil, Jesus still can't do anything about it. Jesus has already done all He is going to do about the devil.