Re: Mark 9:38-41. “Teacher,” said John, “we saw a man driving out demons in your name and we told him to stop, because he was not one of us.” “Do not stop him,” Jesus said. “No one who does a miracle in my name can in the next moment say anything bad about me, for whoever is not against us is for us. I tell you the truth, anyone who gives you a cup of water in my name because you belong to Christ will certainly not lose his reward.”
In this passage John appears concerned about some nonbelievers (“not one of us”) casting out demons in Jesus’ name, and tells them to stop. Jesus rebukes them for doing so, and goes on to imply some church recognition of these (apparent) nonbelievers (“for whoever is not against us is for us”). Is Jesus indicating there is a reward for nonbelievers friendly/helpful toward the Church and it’s members? Am I reading this correctly?
I view this passage somewhat more narrowly, that John was saying the man driving out demons was not one of the Disciples, and therefore ought not be acting like one. Remember, the disciples themselves had only recently failed in their attempts to drive a demon out of an epileptic boy (Mark 9:17-18) and were perhaps indignant that an outsider would try.
As for the cup of cold water, the assumption is that anyone being kind to a follower of Christ in those times when Jesus was thought to be a blasphemer worthy of death, would have to be a believer himself. In the parable of the Sheep and Goats of Matt. 25:31-46 the Lord told us that the same conditions will prevail at the end of the age.
Since salvation is based on what we believe and not how we behave, it’s unlikely that He would have been hinting at some kind of reward for non-believers.