What does Matthew 17:19 mean?
Jesus has cast a demon from a boy (Matthew 17:18). It was causing symptoms like epilepsy, including seizures and foaming at the mouth. Unlike "normal" epilepsy, however, these events frequently happen in crucial moments, throwing the boy into fire and water. Jesus was not available when the boy first arrived with his father. He was up on a mountain with Peter, James, and John (Matthew 17:1). The remaining nine of the twelve disciples (Matthew 10:1–4) attempted to cast the demon out themselves, as Jesus had given them the power and authority to do (Matthew 10:8). They failed.Jesus responded to their failure with exasperation, lumping them in with a "faithless and twisted" generation (Matthew 17:17). Now, the disciples want to understand what went wrong. They sincerely attempted to cast the demon out, and they don't know why they were unable to do so. They come to Jesus privately, after they are away from the crowd, and ask Him in all earnestness why they couldn't do it. He will explain the heart of the issue in the following verse.