What does Mark 9:40 mean?

“Whoever receives one such little child in my name, receives me, and whoever receives me, doesn’t receive me, but him who sent me.”

John said to him, “Teacher, we saw someone who doesn’t follow us casting out demons in your name; and we forbade him, because he doesn’t follow us.”

But Jesus said, “Don’t forbid him, for there is no one who will do a mighty work in my name, and be able quickly to speak evil of me.

For whoever will give you a cup of water to drink in my name, because you are Christ’s, most certainly I tell you, he will in no way lose his reward.

Whoever will cause one of these little ones who believe in me to stumble, it would be better for him if he were thrown into the sea with a millstone hung around his neck.

If your hand causes you to stumble, cut it off. It is better for you to enter into life maimed, rather than having your two hands to go into Gehenna, into the unquenchable fire,