Jesus takes Peter, James and John up a high mountain. There his appearance changes: his clothes become dazzling white, and Elijah and Moses appear talking with him. Peter suggests building three shelters, not knowing what to say because they are terrified. A cloud overshadows them and a voice says that Jesus is the beloved Son and that they should listen to him. Suddenly they see only Jesus. On the way down he orders them to tell no one until the Son of Man has risen from the dead, and they discuss what that means. Jesus clarifies that Elijah has already come, referring to John the Baptist.
Below, a crowd surrounds the other disciples, who have been unable to cast out a mute spirit from a boy. The father describes how the spirit throws him into fire and water. He asks Jesus to help if he can; Jesus replies that all things are possible for one who believes. The father cries out that he believes and asks for help with his unbelief. Jesus rebukes the spirit, which comes out with convulsions, and lifts the boy up. Alone with the disciples, he explains that this kind comes out only by prayer.
Through Galilee, Jesus announces a second time that he will be delivered up, killed and rise, but they do not understand. In Capernaum he finds that they had been arguing about who was greatest; he takes a child and teaches that whoever wants to be first must be servant of all, and that whoever receives such a child receives him. John tells him they saw someone casting out demons in his name and stopped him; Jesus says not to forbid him, for whoever is not against them is for them. He warns about causing little ones to stumble, about cutting off what causes sin, about Gehenna and about salt.