We need to understand 9:38-50 in the light of the vision given in 8:27—9:13 concerning Christ, His death, and His resurrection. Apart from that vision, we do not have the way to understand this section of the Gospel of Mark. The key that opens these verses is Christ with His death and resurrection.
We have pointed out that in 9:38 John told the Lord Jesus that they saw someone casting out demons in His name who did not follow them, and they forbade him, because he was not following them. It seems that John was saying, “This man was casting out demons in Your name, Lord. Yet, he would not follow us. He is divisive, sectarian. Because he causes trouble, we forbade him to cast out demons in Your name. I told him that either he should come along with us, or he should stop casting out demons in Your name.”
In this situation could John say that he was living Christ, that now it was no longer he, but Christ? Certainly not. Had John been terminated by Christ’s death, and had His resurrection been wrought into him? Not at all! In 9:38 John was still a natural son of thunder. He was still in himself, even in an enlarged self. When the Lord was speaking to the disciples concerning humility, John even went on in verse 38 to change the subject.
The Lord’s reply in verse 39 must have come as a great surprise to John: “Do not forbid him, for there is no one who shall do a work of power in My name and be able soon to speak evil of Me.” Here the Lord Jesus was saying to John, “You should not forbid him. He is not against Me; rather, he is for Me. All the believers are mine.”
In verse 41 the Lord went on to say, “For whoever gives you a cup of water to drink in My name because you are Christ’s, truly I say to you that he shall by no means lose his reward.” Here the Lord may have been saying, “Instead of forbidding this one to cast out demons in My name, you should give him a cup of water to drink. If he serves one of you with a cup of water, this will be remembered by Me. Anyone who gives you a cup of water to drink in My name will receive a reward in the coming age.”
In verse 42 the Lord goes on to speak a serious word about causing to stumble those who believe in Him: “And whoever stumbles one of these little ones who believe, it is better for him if a heavy millstone were hung around his neck, and he be thrown into the sea.” How serious it is to cause to stumble those who believe in the Lord! John may have been shocked at this word concerning the seriousness of causing another believer to stumble. He might have said to himself, “If I cause another believer to stumble, my future may be worse than that of someone who has a millstone hung around his neck and is thrown into the sea.”
In verses 43 through 48 the Lord turns from the matter of causing others to stumble to causing ourselves to stumble. He points out that we may be caused to stumble by our hand, foot, or eye. It is serious to cause another believer to stumble, and it is also serious for us to be caused to stumble by any part of our fleshly body. The seriousness of this is indicated by the fact that if we are caused to stumble by a member of our body, we may be thrown into Gehenna, into unquenchable fire.