When Jesus, Peter, James, and John descend from the mountain, they meet a large crowd. Something is wrong. Scribes are gathered around the disciples, arguing with them. The people are quite surprised to see Jesus, and they run to greet him. “What are you arguing about with them?” he asks.​—Mark 9:16.

A man from the crowd kneels before Jesus and explains: “Teacher, I brought my son to you because he has a speechless spirit. Wherever it seizes him, it throws him to the ground, and he foams at the mouth and grinds his teeth and loses his strength. I asked your disciples to expel it, but they were not able to do so.”​—Mark 9:17, 18.

Apparently, the scribes are criticizing the disciples because of their failure to heal the boy, perhaps ridiculing their efforts. So instead of replying to the distraught father, Jesus addresses the crowd, saying: “O faithless and twisted generation, how long must I continue with you? How long must I put up with you?” These strong words certainly apply to the scribes who have been making trouble for his disciples in his absence. Turning to the distressed father, Jesus says: “Bring him here to me.”​—Matthew 17:17.

As the boy approaches Jesus, the demon that possesses him knocks him to the ground and throws him into a violent convulsion. The boy keeps rolling on the ground, foaming at the mouth. “How long has this been happening to him?” Jesus asks the father. He answers: “From childhood on, and often it would throw him into the fire and also into the water to destroy him.” The man pleads: “If you can do anything,  have pity on us and help us.”​—Mark 9:21, 22.

The father is desperate, because even Jesus’ disciples have not been able to help. In response to the man’s desperate appeal, Jesus gives the encouraging assurance: “That expression, ‘If you can’! Why, all things are possible for the one who has faith.” Immediately the father cries out: “I have faith! Help me out where I need faith!”​—Mark 9:23, 24.

Jesus notices the crowd running toward him. With all of these looking on, Jesus rebukes the demon: “You speechless and deaf spirit, I order you, get out of him and do not enter into him again!” In departing, the demon causes the boy to scream and have many convulsions. Then the boy lies there motionless. Seeing this, many people say: “He is dead!” (Mark 9:25, 26) But when Jesus takes the boy’s hand, he rises and is “cured from that hour.” (Matthew 17:18) Understandably, the people are astonished at what Jesus is doing.

Earlier, when Jesus sent the disciples forth to preach, they were able to expel demons. So now, privately in a house, they ask him: “Why could we not expel it?” Jesus explains that it was because of their lack of faith, saying: “This kind can come out only by prayer.” (Mark 9:28, 29) Strong faith along with prayer for God’s empowering help was needed to expel the powerful demon.

Jesus concludes: “Truly I say to you, if you have faith the size of a mustard grain, you will say to this mountain, ‘Move from here to there,’ and it will move, and nothing will be impossible for you.” (Matthew 17:20) How powerful faith can be!

Obstacles and difficulties that block progress in Jehovah’s service may seem to be as insurmountable and irremovable as a literal mountain. Yet, if we cultivate faith, we can overcome such mountainlike obstacles and difficulties.