17 And someone from the crowd answered him, "Teacher, I brought my son to you, for he has a spirit that makes him mute. 18 And whenever it seizes him, it throws him down, and he foams and grinds his teeth and becomes rigid. So I asked your disciples to cast it out, and they were not able." 19 And he answered them, "O faithless generation, how long am I to be with you? How long am I to bear with you? Bring him to me." 20 And they brought the boy to him. And when the spirit saw him, immediately it convulsed the boy, and he fell on the ground and rolled about, foaming at the mouth. 21 And Jesus asked his father, "How long has this been happening to him?" And he said, "From childhood. 22 And it has often cast him into fire and into water, to destroy him. But if you can do anything, have compassion on us and help us." 23 And Jesus said to him, "'If you can'! All things are possible for one who believes." 24 Immediately the father of the child cried out[1] and said, "I believe; help my unbelief!" 25 And when Jesus saw that a crowd came running together, he rebuked the unclean spirit, saying to it, "You mute and deaf spirit, I command you, come out of him and never enter him again." 26 And after crying out and convulsing him terribly, it came out, and the boy was like a corpse, so that most of them 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.