Citations: Mark 9:14-29 (fullest) || Matthew 17:14-21 || Luke 9:37-43, immediately follows the Transfiguration; the glory on the mountain meets desperate need in the valley.
Narrative
Coming down from the Transfiguration, Jesus finds a crowd and his disciples in a dispute, unable to help a boy. The father explains: "Teacher, I brought to you my son, who has a mute spirit. Wherever it seizes him, it throws him down; he foams, grinds his teeth, and becomes rigid. I asked your disciples to cast it out, and they couldn't." (The symptoms, convulsions, foaming, falling, sometimes into fire or water, have long been described as epilepsy; the Gospels frame the case as a spirit.)
Jesus: "Unbelieving generation, how long shall I be with you? How long shall I bear with you? Bring him to me." The spirit immediately convulses the boy. Jesus asks how long it has been; "From childhood" … "But if you can do anything, have compassion on us and help us." Jesus: "If You can? echoed Jesus. All things are possible to him who believes!" (BSB, which follows the earlier manuscripts here; WEB reads "If you can believe") The father cries out, "I believe; help my unbelief!" Jesus rebukes the unclean spirit and commands it out; it cries, convulses the boy terribly, and leaves him "like a corpse," so that many say he is dead. But Jesus takes him by the hand and lifts him up.
Privately the disciples ask, "Why couldn't we cast it out?" Jesus answers, "This kind can come out by nothing but by prayer and fasting" (some manuscripts add "and fasting").
Theological significance
Faith and its weakness, the honest prayer. The father's cry, "I believe; help my unbelief!" is one of Scripture's truest pictures of real faith: not flawless certainty but a trust that admits its own gaps and asks Jesus to make up the difference. Jesus throws the father's tentative "if you can" back at him, the question is not Jesus' ability but whether the man will believe, and then answers the imperfect faith anyway.
Glory above, need below. Placed right after the Transfiguration, the scene contrasts the mountaintop vision with the valley of human anguish and disciple-failure, and shows where Jesus' authority is meant to operate.
The disciples' failure. They had been given authority to cast out demons (Mark 6:7,13), yet here they fail. Jesus diagnoses prayerlessness / "little faith", "this kind" yields only to dependence on God, not to technique or past success.
Textual + framing notes (open). Several early manuscripts lack "and fasting" (Mark 9:29) and the parallel Matthew 17:21 verse; modern translations often bracket them. And the case sits at the meeting point of the demonic and the medical in the ancient world, The Gospels' framing is reported here (a spirit) and notes the long-observed epileptic symptomology without collapsing one into the other.
Theological framing (multiple views)
Read across traditions as a lesson on the nature of faith (sincere yet weak, made effective by Jesus) and on prayer-dependent ministry. Views differ on how to relate the spirit-language to the medical description; The text's framing and the observed symptoms are set side by side here, committing to neither a purely naturalistic nor a purely supernatural reduction.