17 A man out of the crowd answered, "Teacher, I brought my mute son, made speechless by a demon, to you. 18 Whenever it seizes him, it throws him to the ground. He foams at the mouth, grinds his teeth, and goes stiff as a board. I told your disciples, hoping they could deliver him, but they couldn't." 19 Jesus said, "What a generation! No sense of God! How many times do I have to go over these things? How much longer do I have to put up with this? Bring the boy here." 20 They brought him. When the demon saw Jesus, it threw the boy into a seizure, causing him to writhe on the ground and foam at the mouth. 21 He asked the boy's father, "How long has this been going on?" 22 Many times it pitches him into fire or the river to do away with him. If you can do anything, do it. Have a heart and help us!" 23 Jesus said, "If? There are no 'ifs' among believers. Anything can happen." 24 No sooner were the words out of his mouth than the father cried, "Then I believe. Help me with my doubts!" 25 Seeing that the crowd was forming fast, Jesus gave the vile spirit its marching orders: "Dumb and deaf spirit, I command you - Out of him, and stay out!" 26 Screaming, and with much thrashing about, it left. The boy was pale as a corpse, so people started saying, "He's 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.