What does Mark 9:41 mean?
Jesus continues to redefine the type of community He expects His followers to foster. The members are not the powerful but those He sends, whether they be grown, empowered disciples (Mark 6:7–13) or children (Mark 9:36–37), or even, to some extent, as-yet outsiders who have caught a glimpse of Jesus' power (Mark 9:38–40). In response, His followers shouldn't expect honor like the Pharisees (Matthew 6:5) but rejection, suffering (Mark 8:34), and maybe a glass of water. The reward Christians will receive is a heavenly treasure they can't imagine (Matthew 5:12), not the accolades of men (Matthew 6:2).We get too caught up in specifics, sometimes. Churches and ministries should not affirm false beliefs or overlook sin to receive support for God's work. We can, however, graciously accept aid from someone who sees what we do and wants to help. The disciples are ready to reject a man who is at least joining in the fight against satanic forces. Jesus infers there will come a time where the situation is so difficult even a glass of water will be a great blessing and worthy of reward. It's foolish to reject that water just because the one offering it has different theological beliefs.
A few short years after this, Jews and Romans will hunt, try, and kill Christians (Acts 8:1–3). The Jews, at least, believe their violence is in service to God, just as the Pharisees of Mark 3:22–27 think. Jesus expects us to be willing to make great sacrifices for Him (Mark 8:34), with little earthly reward or help. We should be grateful when that help comes.