17 Then one of the crowd answered and said, "Teacher, I brought You my son, who has a mute spirit. 18 And wherever it seizes him, it throws him down; he foams at the mouth, gnashes his teeth, and becomes rigid. So I spoke to Your disciples, that they should cast it out, but they could not." 19 He answered him and said, "O faithless generation, how long shall I be with you? How long shall I bear with you? Bring him to Me." 20 Then they brought him to Him. And when he saw Him, immediately the spirit convulsed him, and he fell on the ground and wallowed, foaming at the mouth. 21 So He asked his father, "How long has this been happening to him?" And he said, "From childhood. 22 And often he has thrown him both into the fire and into the water to destroy him. But if You can do anything, have compassion on us and help us." 23 Jesus said to him, "If you can believe, all things are possible to him who believes." 24 Immediately the father of the child cried out and said with tears, "Lord, I believe; help my unbelief!" 25 When Jesus saw that the people came running together, He rebuked the unclean spirit, saying to it, "Deaf and dumb spirit, I command you, come out of him and enter him no more!" 26 Then the spirit cried out, convulsed him greatly, and came out of him. And he became as one dead, so that many said, "He is dead."
Matthew Henry's Commentary on Mark 9:17-26
Commentary on Mark 9:14-29
(Read Mark 9:14-29)
The father of the suffering youth reflected on the want of power in the disciples; but Christ will have him reckon the disappointment to the want of faith. Very much is promised to our believing. If thou canst believe, it is possible that thy hard heart may be softened, thy spiritual diseases may be cured; and, weak as thou art, thou mayest be able to hold out to the end. Those that complain of unbelief, must look up to Christ for grace to help them against it, and his grace will be sufficient for them. Whom Christ cures, he cures effectually. But Satan is unwilling to be driven from those that have been long his slaves, and, when he cannot deceive or destroy the sinner, he will cause him all the terror that he can. The disciples must not think to do their work always with the same ease; some services call for more than ordinary pains.