20 And they brought the boy to him. When the spirit saw him, immediately it convulsed the boy, and he fell on the ground and rolled about, foaming at the mouth. 21 Jesus asked the father, "How long has this been happening to him?" And he said, "From childhood. 22 It has often cast him into the fire and into the water, to destroy him; but if you are able to do anything, have pity on us and help us." 23 Jesus said to him, "If you are able!-All things can be done for the one who believes." 24 Immediately the father of the child cried out, "I believe; help my unbelief!"
Matthew Henry's Commentary on Mark 9:20-24
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.