Matthew 17:21

Howbeit, this kind goeth not out but by prayer and fasting.

After the healing of the demoniac, Jesus went into a house. And there, where they were by themselves, the disciples gain enough courage to ask Him in regard to their failure. The fact stood before them: They had not been able to cast him out. The question seems to imply that the experience was exceptional; in other cases they had not had this difficulty, Luke 10:17. Jesus very frankly tells them the trouble. Their faith, their trust in God, had not been equal to the occasion; it had been too small to effect a cure in this instance. Probably the disciples, who formerly had cast out devils in the Lord's name and by His authority, had attempted to exorcise, trusting in their own strength. Not redeeming faith is meant here, of course, but a firm reliance in God's power and promises. For if such trusting faith is present, though it be as small as a single grain of mustard-seed by comparison, though its quantity represent the minimum of such trust, yet it could perform miracles as yet undreamed of by them, such as the moving of mountains. Nothing is impossible to such faith. If we have God's command and promise in our undertaking, then we should firmly rely upon His almighty strength, knowing that we shall be able to perform what He has given us to do. See chap. 21:21; Mark 11:23. Things that seem impossible before men, undertakings that are frankly jeered at as dreams of visionaries, works of mercy or other projects in the Church that seemed hopeless from the start, have been carried out successfully because of a firm reliance in the justness of the cause and in the help of the Lord above. The Lord adds finally, for the information of His disciples in other cases of this kind, that fasting and prayer are helpful in bringing about the desired result. The more difficult the question that confronts the Christian, the more firmly must he cling to God's promises. Whether Satan be actually present in the form of a very malignant and baffling disease, or whether he attempt to hinder the work of Christ in His Church by all manner of obstructions, earnest, devout prayer is an ally that can be depended upon to secure the needed help from above, to put the enemy to flight, and to gain the day for the cause of Christ.