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.
18. And wheresoever he taketh him, he teareth him; and he foameth, and gnasheth with his teeth, and pineth away—rather, "becomes withered," "dried up," or "paralyzed"; as the same word is everywhere else rendered in the New Testament. Some additional particulars are given by Luke, and by our Evangelist below. "Lo," says he in Lu 9:39, "a spirit taketh him, and he suddenly crieth out; and it teareth him that he foameth again, and bruising him hardly [or with difficulty] departeth from him."
and I spake to thy disciples that they should cast him out; and they could not—Our Lord replies to the father by a severe rebuke to the disciples. As if wounded at the exposure before such a multitude, of the weakness of His disciples' faith, which doubtless He felt as a reflection on Himself, He puts them to the blush before all, but in language fitted only to raise expectation of what He Himself would do.