Mark 9:38

This is the only place where the synoptic writers mentioned John speaking out alone. John spoke for the other disciples in the house (Mark 9:33).

Evidently the exorcist was a believer in Jesus though not one of the Twelve or possibly not even one who spent much time following Jesus around. He evidently commanded demons to leave the people they afflicted by using Jesus’ name. The Twelve apparently did not mind that this man claimed Jesus’ authority to exorcize demons. They objected to his actions because Jesus had not commissioned him to do so as He had the Twelve (Mark 3:14-15). Perhaps his success and the recent failure of the nine disciples irritated them further. In view of what Jesus had just said about receiving little children, John wondered if the Twelve had done right in rebuking the man. They had tried to protect Jesus’ honor by rebuking him (cf. Numbers 11:26-29).

"It is striking . . . that after each of the three major prophecies of the passion the evangelist inserts the response of one of the three disciple who were closest to Jesus: Peter (Ch. Mark 8:32 f.), John (Ch. Mark 9:38), and James, with John (Ch. Mark 10:35-37). Mark shows in this way that even the most privileged of the disciples failed to understand what the passion signified for their life and mission." [Note: Lane, p. 342.]