Expositor's Bible Commentary 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)

John’s use of “we” shows that he was speaking for all the disciples. This is the only time Mark mentions John alone. The exorcist had been driving out demons in Jesus’ name, i.e., with his authority. What irked the disciples was that, though he was not one of them, he was being successful at it! What made things even worse was that they doubtless remembered their own failure to exorcise the demon from the epileptic (cf. 9:14–18). The strange exorcist must have been a believer. Since he was not a part of the exclusive company of the Twelve, they took it on themselves to stop him.