Today's verses are Mark 9:38-40: "John said to him, 'Teacher, we saw someone casting out demons in your name, and we tried to stop him, because he was not following us.' But Jesus said, 'Do not stop him, for no one who does a mighty work in my name will be able soon afterward to speak evil of me. For the one who is not against us is for us.'" They key phrase here from John to Jesus about people casting out demons in Jesus' name is this one: "he was not following us." Whoever this person was, John didn't see him as a part of the Twelve. He wasn't on their team. Therefore, John thought he needed to cease what he was doing. Jesus responded that anyone who does a work in his name won't be able to soon thereafter speak ill of him. "For the one who is not against us is for us," he said.
The apostle Paul makes a similar argument in Philippians 1:17-18. Jesus is saying to his disciples to focus on their task and be slow to criticize othes who say they are his followers. Leave this judgment to God, he was saying, and avoid snap judgments of those who aren't a part of your group. If someone says Jesus is Lord of their lives, then this person is on your same team as a Christian. He may be called to a different work for Jesus' glory, done in a different way than you. But if he uses the name of Jesus, he or she is a teammate. Treat them as such, Jesus was saying.
Jesus knew how easy it is to choose sides and criticize anyone not like us or not doing it our way. When we criticize, we create pride and arrogance in our own hearts. It may show envy, that someone else is being more successful than we are. The key seems to be if they use the name of Jesus as the authoritative name that guides their ministry. If so, be slow to criticize!
Does this mean Christians should never raise concerns about people who use Jesus' name but may be false teachers? Absolutely not! He instructs us in Matthew 7:15ff about the need to beware of false prophets who are out to use Jesus' followers for their glory. They may even use his name. But it's always for their glory and gain, not Jesus' glory and gain. We are carefully to examine their fruit to see if it matches their "root", Jesus. We're simply to be very careful in criticizing them and saying they don't belong to Jesus. After all, only God truly knows the heart.
Remember: Jesus desires that we be one in him, as he and the Father are one together (John 17:21). Therefore, be slow to criticize other followers of Jesus.