Charles Ellicott Commentary Mark 9:38

"John said unto him, Teacher, we saw one casting out demons in thy name; and we forbade him, because he followed not us." — Mark 9:38 (ASV)

And John answered him.—The incident that follows, omitted by St. Matthew, is recorded by St. Luke in the same connection. It indicates something of the same zeal as that which prompted the desire that fire might come from heaven to consume the Samaritans who refused to receive our Lord (Luke 9:52). The words were an “answer” to what our Lord had said, to the extent that they were suggested by it.

The disciple desired to show, as in self-vindication, that he not only “received” his Master, but that he was unwilling to “receive” anyone who did not openly follow Him as a disciple. The fact he speaks of is significant historically, indicating that one of the effects of our Lord’s work had been to stir up and quicken the spiritual powers of men outside the range of the company of disciples that gathered round Him. They believed in Him, or they would not have used His Name. They were fellow-workers with Him, for they were seeking to rescue the souls of men from frenzy and despair. Their faith was effective, for, as the narrative implies, they not only claimed the power to cast out demons, but did cast them out. The case, it is obvious, was on an entirely different footing from that of the sons of Sceva, in Acts 19:13-14, which at first sight seems to resemble it.