This kind goeth not out, [1] By this expression Christ reproved the negligence of certain persons, in order to inform them that it was not an ordinary faith which was required; for otherwise they might have replied that they were not altogether destitute of faith The meaning therefore is, that it is not every kind of faith that will suffice, when we have to enter into a serious conflict with Satan, but that vigorous efforts are indispensably necessary. For the weakness of faith he prescribes prayer as a remedy, to which he adds fasting by way of an auxiliary. "You are effeminate exorcist," said he, "and seem as if you were engaged in a mock-battle got up for amusement; [2] but you have to deal with a powerful adversary, who will not yield till the battle has been fought out. Your faith must therefore be excited by prayer, and as you are slow and languid in prayer, you must resort to fasting as an assistance." [3] Hence it is very evident how absurdly the Papists represent fasting to be the specific method of driving away devils, since our Lord refers to it for no other reason than to stimulate the earnestness of prayer. When he says that this kind of devils cannot be cast out in any other way than by prayer and fasting, he means that, when Satan has taken deep root in any one, and has been confirmed by long possession, or when he rages with unbridled fury, the victory is difficult and painful, and therefore the contest must be maintained with all our might.

Footnotes

1 - "Cest espece [de diablos] ne sort point;" -- "this kind [of devils] goeth not out."

2 - "Vous y venez ainsi qu'a un combat de petits enfans, et comme s'il n'estoit question que de s'escarmoucher pour passe-temps." -- "You come to it as if it were to a fight of little children, and as if you had nothing to do but to skirmish for amusement."

3 - "Comme une aide pour vous exciter et enflamber;" -- "as an assistance to excite and inflame you."

Howbeit, this kind - This kind means this kind of devils - this species of possession. Where they have had long possession where they produce such painful, fixed, and alarming effects, they can be expelled only in connection with prayer and fasting.
Goeth not out but by prayer and fasting - That is, in order to work miracles of this kind to cast out devils in cases so obstinate and dreadful as this, faith of the highest kind is necessary. That faith is produced and kept vigorous only by much prayer, and by such abstinence from food as fits the mind for the highest exercises of religion, and leaves it free to hold communion with God.

This kind goeth not out but by prayer, etc. - Τουτο το γενος, this kind, some apply to the faith which should be exercised on the occasion, which goeth not out, doth not exert itself, but by prayer and fasting; but this interpretation is, in my opinion, far from solid. However, there is great difficulty in the text. The whole verse is wanting in the famous Vatican MS., one of the most ancient and most authentic perhaps in the world; and in another one of Colbert's, written in the 11th or 12th century. It is wanting also in the Coptic, Ethiopic, Syriac, Hieros., and in one copy of the Itala. But all the MSS. acknowledge it in the parallel place, Mark 9:29, only the Vatican MS. leaves out νηϚεια, fasting. I strongly suspect it to be an interpolation; but, if it be, it is very ancient, as Origen, Chrysostom, and others of the primitive fathers, acknowledged it. But while candour obliges me to acknowledge that I cannot account for the fact here alleged, that a certain class or genus of demons cannot be expelled but by prayer and fasting, while others may be ejected without them, I can give a sense to the passage which all my readers will easily understand: viz. that there are certain evil propensities, in some persons, which pampering the flesh tends to nourish and strengthen; and that self-denial and fasting, accompanied by prayer to God, are the most likely means, not only to mortify such propensities, but also to destroy them. For other remarkable circumstances relative to this case, see the notes on Mark 9:17, etc.

(4) Howbeit this kind goeth not out but by (h) prayer and fasting.
(4) The remedy against distrust.
(h) To help us to understand the watchfulness and diligence of earnest prayer, which cannot be without sobriety.

Howbeit, this kind goeth not out,.... The Vulgate Latin renders it, "is not cast out"; and so do the Arabic version, and Munster's Hebrew Gospel; and which confirm the more commonly received sense of these words, that they are to be understood of that kind of devils, one of which was cast out of the lunatic, and was of the worst sort, of a fierce and obstinate kind; and having had long possession, was not easily ejected: and that there is a difference in devils, some are worse and more wicked than others, is clear from Matthew 12:45 and not of that kind of miracles, or kind of faith to the working of such miracles. Moreover, the above versions, as they fitly express the word here used; see Mark 9:17 compared with Matthew 15:17. So they pertinently set forth the dispossession of devils, who do not go out voluntarily, but by force; and this sort could not be ejected,
but by fasting and prayer: that is, in the exercise of a miraculous faith, expressed in solemn prayer to God, joined with fasting. It seems that Christ not only suggests, that faith was greatly wanting in his disciples; for which reason they could not cast out the devil, and heal the lunatic; but they had been wanting in prayer to God, to assist them in the exercise of their miraculous gifts; and that whilst Christ, and the other three disciples were on the mount, they had been feasting and indulging themselves with the people, and so were in a very undue disposition of mind, for such extraordinary service, for which our Lord tacitly rebukes them. This agrees with the notions of the Jews, who think that, by fasting, a divine soul (f) , "may obtain that which is sought for"; and that among other things, for which a private person may afflict himself with fasting, this is one, , "because of an evil spirit" (g); which they think may be got rid of this way.
(f) Jacchiades in Daniel. x. 3. (g) T. Bab. Taanith, fol. 22. 2. Maimon. Hilch. Taaniot, c. 1. sect. 6.

But this kind . . . but by prayer and fasting. Compare Mark 9:29. Only by devout waiting before the Lord for strength. Such strength is always needful to the victories of faith. Often, too, we have demons, envy, pride, covetousness, a revengeful spirit, that must be cast out by prayer.

This kind of devils - goeth not out but by prayer and fasting - What a testimony is here of the efficacy of fasting, when added to fervent prayer! Some kinds of devils the apostles had cast out before this, without fasting.