This verse, according to the best authorities, should begin simply, John said unto him—although in St. Luke (Luke 9:49) they stand, "And John answered and said"—Master, we saw one casting out devils in thy name: and we forbade him, because he followed not us.
The casting out of evil spirits was one of the foremost signs of apostleship; and what surprised St. John was that one who followed not Christ should have been able to work this miracle—a miracle in which, it will be remembered, the disciples had recently failed.
It thus appears that our Lord's teaching had been so influential, that some, not reckoned amongst his disciples, had shown this proof of a strong and overpowering faith. We know that there were those in our Savior's time, of Jewish race, who cast out devils (Matthew 12:27).
And Justin Martyr, in his 'Dialogue with Trypho the Jew,' states that while exorcism, as practiced by the Jews, often failed when it was attempted to be exercised "by the God of Abraham, Isaac, and Jacob," was eminently successful when administered "by the name of the Son of God, who was born of a virgin and crucified under Pontius Pilate" (c.
85). That spirit has power over spirit in many mysterious ways is one of those truths which science has not yet been able to explain. To return, however, to the instance here alluded to by St. John, it should be observed that they who acted thus had faith in Christ; and that by thus acting with him and for him, though not amongst his recognized followers, they contributed towards his honor who, by means of these imperfect instruments, carried out the great purpose of his manifestation, namely," to destroy the works of the devil."
Then further, the disciples forbade them not out of envy or hatred, but out of zeal for Christ, as though they were thus serving his cause and upholding his honor. But this was" a zeal, not according to knowledge."
They had forbidden them, without having first taken counsel of their Master.