But notice they had been “working for salvation”, per Charles’ instruction. THAT’S the scary part, they thought they had obligated God.
‘Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name?’
Not a word about repentance, sorrow for their own sins, true conversion of heart, or seeking the mercy and grace of God. It's all, and only, "doing stuff" in God's name in front of other people.