There is no neutral ground when it comes to following Jesus. You are either with him or against Him. The disciples understood this and sought clarity when it comes to who is in and who is out of the Kingdom of God. Mark records the story of John seeking to discover if he did the right thing when he rebuked a man for casting out demons in Jesus name. The rebuke had little to do with the exorcism and much to do with not being a part of Jesus’ twelve disciples. Mark only records that the exorcist did his work in Jesus name. John and the others could not stand that he would do such a thing without Jesus’ direct approval or without being one of the twelve so he rebuked the man, shutting him down. They thought they were protecting Jesus’ honor. It is easy to imagine also that seeing the success of one not “close” to Jesus must have been frustrating in light of their recent failure to deliver a man from an unclean spirit. Jesus’ response was not what they expected.