There are several classic stories packed into this chapter. First we have the Transfiguration, where Peter, James and John see Jesus transformed into dazzling white with Elijah and Moses. After Jesus goes back to normal, they have a puzzling conversation:
Then they asked him, ‘Why do the scribes say that Elijah must come first?’ He said to them, ‘Elijah is indeed coming first to restore all things. How then is it written about the Son of Man, that he is to go through many sufferings and be treated with contempt? But I tell you that Elijah has come, and they did to him whatever they pleased, as it is written about him.’
But anyway. We move on to an unusually detailed exorcism story. A man's son is having seizures of some sort, and the disciples have tried and failed to heal him. Jesus, somewhat atypically, asks how long the son's been afflicted. Since childhood, he's told, and it's sometimes tried to kill him. The father says, "... if you are able to do anything, have pity on us." Jesus answers that all things can be done for one who believes, and the father returns with the famous line, "I believe; help my unbelief!"
It's one of those great lines because it seems contradictory, and yet it's so true. There are a lot of points on the continuum between believing and not believing, and the story sends the message that Jesus is willing to help you out even if you haven't fully arrived.
Jesus heals the boy, though it's traumatic. At first the son is so weakened the bystanders think he's dead. The disciples ask Jesus later why they couldn't cast out the demon. He answers, "This kind can come out only through prayer."
It's a puzzling answer. It implies that there are categories of demons and this was a particularly tough one. But it's also odd because there isn't any sign in the story of Jesus or the boy praying; Jesus just commands the spirit to leave, as usual. I suppose if anybody was praying it was the father, but it seems like everybody who asks Jesus for help "prays" in that fashion. And anyway, I thought all the healings involved prayer of some sort, in calling on God's help.
At any rate, Jesus foretells his death and resurrection again, and the group goes to a house to stay over. They have a very disjointed conversation that underlines the strung-together quality of the gospels, ranging from the disciples' argument over who's the greatest to the protection of children to the "if your hand causes you to stumble, cut it off" litany. In the middle, though, there's an interesting and less well-known conversation where the disciples say somebody they don't know was doing healings in Jesus' name and they'd tried to stop him. Jesus answers:
Do not stop him; for no one who does a deed of power in my name will be able soon afterward to speak evil of me. Whoever is not against us is for us. For truly I tell you, whoever gives you a cup of water to drink because you bear the name of Christ will by no means lose the reward.