Ask for a jug of water at a restaurant; it is given free of charge. Water in this case is taken for granted. Fresh water means life when a person is on a high sea or in a desert. Jesus told His disciples, a glass of water given in God's Name, has everlasting value. God is generous in His reward. Different methods of judgment lead to different outcomes. We judge the value of the substance, the glass of water itself. God judges not the substance, but the action, the kindness of a person's heart. Great reward is given, not on the matter itself, but on something deeper, an act of kindness, the generosity a person's heart.
John reported that he had stopped a man, who was casting out devils in God's name. Jesus told him: do not stop him. John stopped the man because John judged the man's action according to the norm of his society. The man needed authorization to do such thing. He was a stranger, not one of the apostles, and should not do such work. Jesus allowed the man to work in His Name. Jesus followed not the Roman's way of operating. Jesus judged not the man's membership, but his good intention, the goodness of the man's heart. John worked on the level of inner circle. Jesus welcomed those who showed kindness to others, even though they were not yet members of the apostles.
Anyone who is not against us is for us. v.40.
The apostles now knew there were people who believed, and worked for Jesus, unknown to them, but well known to Jesus. Later on, the apostles learnt about a person who lent Jesus the ass to ride on entering Jerusalem (Mk 11,2); the other one gave Him a room to celebrate the feast of the Passover (Mk 14,15); and another one who provided Him a tomb for His burial (Mk 15,46). These people were unknown to the apostles until afterwards.
Jesus was very strong in His language to those, who became a stumbling block for others to believe in God. He warned them, causing harm to some one's faith would not escape severe punishment in hell. The reference to a human limbs, such as a foot, hand or an eye means, that a part is smaller than a whole. People would feel uneasy about removing a foot or an arm, but human wisdom tells us; it is wise to sacrifice a small part to save the whole body. The removal of a cancer spot on a human body, to save life is a common thing in the medical world.
Jesus told us that whatever good, or bad actions we do in life will have eternal effects. We are happy to receive reward for a simple good act, but deny the liability for bad action. Power seeking in a Christian community is a public scandal. It should be avoided at all cost. These things cause rivalry, separation, and disharmony for a Christian community. They are contrary to Jesus' teaching. It should not happened among Jesus' disciples. Causing others to lose faith in God is a vice, believing in one own knowledge rather than Jesus' teaching. Arrogance is one of the vices. It has no place in God's kingdom. Jesus was very clear, strong, and firm in stopping Devils from speaking of Him. He would not compromise on this, not even allow them to reveal His identity. Becoming a stumbling block for others reveals the weakness of one's faith. Once the faith was weak, that person soon falls into temptations. The very first temptation is to find buddies to take side with him.
We are called to nurture faith, not to destroy faith.