What does Matthew 17:15 mean?
Three of the disciples have returned, with Jesus, from His "transfiguration" on top of a nearby mountain (Matthew 17:1–13). Christ approaches the other nine disciples to find them in an argument with some Jewish scribes. In Mark's account (Mark 9:14–29) this father approaches after Jesus asks what they are arguing about. The man pleads on behalf of his son who suffers from seizures which often cause him to fall into fire or water. Mark and Luke are more direct in ascribing these symptoms to a demon: "…a spirit that makes him mute…throws him down, and he foams and grinds his teeth and becomes rigid" (Mark 9:17–18). And "it convulses him so that he foams at the mouth, and shatters him, and will hardly leave him" (Luke 9:39). Many commentators have described these symptoms as a form of epilepsy brought on by the evil spirit. The detail included here by Matthew strongly implies this is not "just" epilepsy. As the father notes, it so often happens in especially dangerous moments. This fits with the self-destructive nature of demon oppression.While Jesus was gone, this man brought his son to Jesus' nine remaining disciples. The source of the argument with the scribes seems to be their inability to cast the demon out of the boy. Jesus will explain why they were unsuccessful.