421. Is casting out devils a sign of a true Christian?
Yes, it is a sign of a true believer.
These signs shall follow them that believe; In my name shall they cast out devils. Mark 16:17
No, some who don't follow Jesus can cast out devils too.
John answered him, saying, Master, we saw one casting out devils in thy name, and he followeth not us: and we forbad him, because he followeth not us. Mark 9:38
No, many who have cast out devils in Jesus's name are now in hell.
Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works? And then will I profess unto them, I never knew you: depart from me, ye that work iniquity. Matthew 7:22-23