"13 Some Jews who went around driving out evil spirits tried to invoke the name of the Lord Jesus over those who were demon-possessed. They would say, In the name of the Jesus whom Paul preaches, I command you to come out. 14 Seven sons of Sceva, a Jewish chief priest, were doing this. 15 One day the evil spirit answered them, Jesus I know, and Paul I know about, but who are you? 16 Then the man who had the evil spirit jumped on them and overpowered them all. He gave them such a beating that they ran out of the house naked and bleeding."
This happened because they did not really have a firm belief yet.
They were attempting to do something in His name but were not true believers is the way I understand it. To me, it also means I’d best be fully “armoured” in my faith before attempting to battle satan in a no holds barred type UFC match.
I feel like I battle him daily on the little things he uses to mess with me.