Mark 9:28-29. When he was come into the house, his disciples asked him, &c. — See notes on Matthew 17:19-21. This kind can come forth by nothing but by prayer and fasting — “Some doubts have been raised in regard to the meaning of the words, this kind. The most obvious interpretation is, doubtless, that which refers them to the word demon, immediately preceding. But as in the parallel passage in Matthew 17:19, mention is made of faith, as the necessary qualification for dispossessing demons, Knatchbull and others have thought that this kind, refers to the faith that is requisite. But it is an insurmountable objection to this hypothesis, that we have here the same sentiment, almost the same expression, and ushered in with the same words, this kind, though, in what goes before, there is no mention of faith, or of any thing but demon, to which it can refer. It would be absurd to suppose, that the pronouns and relatives in one gospel refer to antecedents in another. Every one of the gospels does indeed give additional information, and in various ways serves to throw light upon the rest. But every gospel must be a consistent history by itself; otherwise, to attempt an explanation would be in vain. Now the argument stands thus: The story related in both gospels is manifestly the same: that the words in question may refer to demon in Matthew, no person who attentively reads the passage can deny; that they cannot refer to faith, but must refer to demon, in Mark, is equally evident. Either, then, they refer to demon in both, or the evangelists contradict one another. Some have considered it as an objection to the above explanation, that it supposes different kinds of demons; and that the expulsion of some kinds is more difficult than that of others. This objection is founded entirely on our own ignorance. Who can say that there are not different kinds of demons? or that there may not be degrees in the power of expelling? Revelation has not said that they are all of one kind, and may be expelled with equal ease.” — Campbell.

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.Said with tears - The man felt the implied rebuke in the Saviour's language; and feeling grieved that he should be thought to be destitute of faith, and feeling deeply for the welfare of his afflicted son, he wept. Nothing can be more touching or natural than this. An anxious father, distressed at the condition of his son, having applied to the disciples in vain, now coming to the Saviour; and not having full confidence that he had the proper qualification to be aided, he wept. Any man would have wept in his condition, nor would the Saviour turn the weeping suppliant away.

I believe - I have faith. I do put confidence in thee, though I know that my faith is not as strong as it should be.

Lord - This word here signifies merely "master," or "sir," as it does often in the New Testament. We have no evidence that he had any knowledge of the divine nature of the Saviour, and he applied the word, probably, as he would have done to any other teacher or worker of miracles.

Help thou mine unbelief - Supply thou the defects of my faith. Give me strength and grace to put "entire" confidence in thee. Everyone who comes to the Saviour for help has need of offering this prayer. In our unbelief and our doubts we need his aid, nor shall we ever put sufficient reliance on him without his gracious help.

28. Why could not we cast him out?Ver. 28. See Poole on "Mark 9:17"

And when he was come into the house,.... Perhaps into the man's house whose child he had healed, or into some other in these parts, for the sake both of retirement and refreshment:

his disciples asked him privately, why could not we cast him out? The nine disciples, who were particularly concerned in this matter, fearing they had lost the power of casting out devils, conferred upon them, inquired of Jesus, when he was alone, why they could not cast the demon out of the child, when they had ejected unclean spirits out of many others; See Gill on Matthew 17:19.

{6} And when he was come into the house, his disciples asked him privately, Why could not we cast him out?

(6) We have need of faith, and therefore of prayer and fasting, in order to cast Satan out of that which belonged to him.