Matthew 17:21
Howbeit this kind goeth not out but by prayer and fasting.
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 ekporeutai, 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} hvqwbm ta gyvt, "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, her xwr ynpm, "because of an evil spirit" {g}; which they think may be got rid of this way.
{f} Jacchiades in Dan. x. 3.
{g} T. Bab. Taanith, fol. 22. 2. Maimon. Hilch. Taaniot, c. 1. sect. 6.