Church Fathers Commentary Matthew 17:19-21

"Then came the disciples to Jesus apart, and said, Why could not we cast it out? And he saith unto them, Because of your little faith: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you. [But this kind goeth not out save by prayer and fasting.]" — Matthew 17:19-21 (ASV)

St. John Chrysostom: The disciples had received from the Lord the power over unclean spirits. When they could not heal the demoniac brought to them, they seem to have had misgivings that they might have forfeited the grace once given to them, which is why they asked their question. They ask it privately, not out of shame, but because of the profound matter they were asking about.

Jesus said to them, “Because of your unbelief.”

St. Hilary of Poitiers: The Apostles had believed, yet their faith was imperfect. While the Lord remained on the mountain and they stayed below with the multitude, their faith had become stagnant.

St. John Chrysostom: From this it is plain that the disciples' faith had grown weak—yet not all of them, for those pillars were there: Peter, James, and John.

St. Jerome: This is what the Lord says in another place: “Whatever you ask in my name, believing, you will receive” (Matthew 21:22; John 16:23). Therefore, when we do not receive, it is not the weakness of the One who gives, but the fault of those who ask.

St. John Chrysostom: It should be known that just as the faith of the one who draws near to receive often provides the miraculous power, so also the power of those who work the miracle is often sufficient, even without the faith of those who seek to receive it.

For example, Cornelius and his household, by their faith, attracted the grace of the Holy Spirit to themselves (Acts 10:4). In contrast, the dead man who was cast into the tomb was revived solely by the power of the holy body (2 Kings 13:21).

It happened that the disciples were weak in faith at that time, for they were still in an imperfect state before the cross. This is why He tells them here that faith is the means for miracles: “Truly I say to you, if you have faith as a grain of mustard seed, you will say to this mountain, ‘Move from here,’ and it will move.”

St. Jerome: Some think that the faith compared to a grain of mustard seed is a little faith, whereas the Apostle says, “If I have such faith that I could remove mountains” (1 Corinthians 13:2). The faith that is compared to a grain of mustard seed is therefore a great faith.

St. Gregory the Great: The mustard seed, unless it is crushed, does not release its qualities. So if persecution befalls a holy man, immediately what had seemed weak and contemptible in him is roused into the heat and fervor of virtue. ¹

Origen of Alexandria: Alternatively, all faith is compared to a grain of mustard seed because faith is viewed with contempt by men and appears to be something poor and insignificant. But when a seed of this kind lands on a good heart as its soil, it becomes a great tree.

The affliction of this lunatic is so great—and Christ is so strong to heal him in the midst of all his evils—that He compares it to a mountain, which cannot be cast out except by the complete faith of the one who desires to heal afflictions of this kind.

St. John Chrysostom: So He not only promises the removal of mountains but goes beyond it, saying, “And nothing will be impossible for you.”

Rabanus Maurus: For faith gives our minds such a capacity for heavenly gifts that whatever we will, we can easily obtain from a faithful Master.

St. John Chrysostom: If you ask, “Where did the Apostles remove mountains?” I answer that they did greater things, bringing many dead to life. It is also told of some saints who came after the Apostles that they have, in urgent necessity, removed mountains.ⁱ

But if mountains were not removed in the Apostles' time, this was not because they could not, but because they would not, as there was no pressing need. The Lord did not say that they would do this, but that they would have the power to do it.

Yet it is likely that they did do this, but it is not recorded, for indeed not all the miracles they performed are written down.

St. Jerome: Alternatively, the “mountain” does not refer to that which we see with our physical eyes, but signifies that spirit which was removed by the Lord from the lunatic—the one who is said by the Prophet to be the corrupter of the whole earth.

Glossa Ordinaria: The meaning, then, is this: “You will say to this mountain”—that is, to the proud devil—“‘Move from here’”—that is, from the possessed body into the sea, meaning into the depths of hell—“‘and it will move; and nothing will be impossible for you’”—that is, no sickness will be incurable. ²

St. Augustine of Hippo: Alternatively, so that the disciples are not lifted up with pride in working their miracles, they are warned by the humility of their faith—symbolized by the grain of mustard seed—to be careful to remove all earthly pride, which is signified by the “mountain” in this passage.

Rabanus Maurus: While He teaches the Apostles how the demon ought to be cast out, He instructs everyone in the regulation of life. He does this so that we may all know that the heavier afflictions—whether from unclean spirits or the temptations of men—can be removed by fasting and prayer, and that the Lord's wrath may also be appeased by this remedy alone. This is why He adds, “However, this kind does not go out except by prayer and fasting.”

St. John Chrysostom: He says this not about lunatics in particular, but about the entire class of demons. For fasting endows a person with great wisdom, makes him like an angel from heaven, and beats down the unseen powers of evil. But prayer is needed as something even more important.

One who prays and fasts as he ought needs little else; he is not covetous but is ready to give alms. For he who fasts is light and active, prays with vigilance, quenches his evil desires, makes God favorable, and humbles his proud self.

The one who prays while fasting has two wings, lighter than the winds themselves. He is not heavy and wandering in his prayers (as is the case with many), but his zeal is like the warmth of fire, and his constancy is like the firmness of the earth. Such a person is most able to contend with demons, for there is nothing more powerful than a man who prays properly.

But if your health is too weak for strict fasting, it is not too weak for prayer. If you cannot fast, you can still abstain from indulgences. This is no small thing and is not very different from fasting.

Origen of Alexandria: If, then, we are ever required to heal those who are suffering from anything of this sort, we should not command them, nor ask them questions, nor even speak as though the unclean spirit could hear us. Instead, we should drive away the evil spirits by our fasting and our prayers.

Glossa Ordinaria: Alternatively, this class of demons—that is, the variety of carnal pleasures—is not overcome unless the spirit is strengthened by prayer and the flesh is weakened by fasting. ³

Remigius of Auxerre: Alternatively, fasting is understood here generally as abstinence not only from food but from all carnal allurements and sinful passions. Similarly, prayer is to be understood in general as consisting of pious and good acts, about which the Apostle speaks: “Pray without ceasing” (1 Thessalonians 5:17).

1. Mor., pref. c. 2
2. interlin.
3. ord.