Matthew 17:19-21; Mark 9:28-29; Luke 17:5-6

Matthew 17:19. Then the disciples coming. The disciples wonder that the power which they once possessed has been taken from them; but they had lost it by their own fault. Christ therefore attributes this want of ability to their unbelief, and repeats and illustrates more largely the statement which he had previously made, that nothing is impossible to faith. It is a hyperbolical mode of expression, no doubt, when he declares that faith removes trees and mountains; but the meaning amounts to this, that God will never forsake us, if we keep the door open for receiving his grace. He does not mean that God will give us every thing that we may mention, or that may strike our minds at random. On the contrary, as nothing is more at variance with faith than the foolish and irregular desires of our flesh, it follows that those in whom faith reigns do not desire every thing without discrimination, but only that which the Lord promises to give. Let us therefore maintain such moderation as to desire nothing beyond what he has promised to us, and to confine our prayers within that rule which he has laid down.

But it may be objected, that the disciples did not know whether or not the Lord was pleased to cure the lunatic. It is easy to reply, that it was their own fault if they did not know; for Christ is now speaking expressly about special faith, which had its secret instincts, as the circumstances of the case required. And this is the faith of which Paul speaks, (1 Corinthians 12:9.) How then came it that the apostles were deprived of the power of the Spirit, which they had formerly exercised in working miracles, but because they had quenched it by their indolence? But what Christ said about special faith, in reference to this particular event, may be extended to the common faith of the whole Church.

21. This kind goeth not out, ³ 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; ⁴ 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." ⁵ 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.