John Calvin's Verse Commentary
Matthew 17:21
21. 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.
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.”
Matthew Poole's Commentary on the Holy Bible
Matthew 17:21
Ver. 19-21. Mark repeats only what we have here Mt 17:19,21. The reason assigned here by our Saviour why his disciples could not cast out this devil, was their unbelief; not their total want, but the weakness of their faith. Christ here again lets us see the power of faith, and the mischief of unbelief. I take the plain sense of the text to be this, That there is nothing which may tend to the glory of God, or to our good, but may be obtained of God by a firm exercise of faith in him. Whether our Saviour here speaketh of a faith of miracles, or no, I will not determine; I rather think that he speaketh here of any true faith: we must have the power and promise of God for its object. The promise of working miracles by a Divine power committed to them, was a particular promise made to the disciples, Mt 10, and so was only the object of their faith. But I take our Saviour's words to extend to a further latitude, though, as to miraculous operations, it was only applicable to them. There is nothing which God hath promised to give or bestow on any but faith will obtain from him, if attended by a fervent prayer, to which fasting is subservient, as preparing us to it. There are some things which are obtained by a stronger faith, and by more fervent and importunate prayers, than others are. A mercy sometimes seem to us to come out of the hand of God with more difficulty, and wrestling for it; but there is nothing within the latitude of a promise, but is to be done and obtained by the vigorous exercise of faith, and by fervent and importunate prayer. The apostles had yet but a weak and imperfect faith, and they had not used such fervent and importunate prayer in this case as they ought to have done; thence did this work appear so difficult unto them.
End.
Then where, did the Lord go first, after this? That He must suffer and be crucified and raised again. So even more our fasting is to be for the Lord, for if the disciples faith was not good enough to cast out this kind of demon, it must take a much greater faith insisted upon by fasting and prayer than we possess within ourselves. Who's faith must we entreat to cast out this kind of demon. It must be the Faith of the Son of God and in setting up the war that would be fought, to fight with the same determinate strength of Christ that He had for fourty days and nights with His Father to begin His journey to completely defeat the devil and all his Adversaries. Where is our victory, not in prayer and fasting but in Christ and Christ alone that is our total and complete clothing of Armour and strength. For the demons said they new who Jesus was and who Paul was, but those that got beaten up and stripped naked were outside of this strength and power. If I go against a demon of this power, I sure don't want to do it without the strength and power of Christ and the Holy Spirit and if it takes fourty days and nights to receive the total and complete surety that I am going in the strength and power of God, I cannot because it would be foolish and God will do what He and with who He wants to deal with this kind of demon. I certainly want to know that this is the will of God and I am going in His Name and Majesty and Strength with the Full Armour of God intact and completely worn as given instructions by our Full Armour Giver.
Truly my fast is my Savior and Lord are unreachable in my flesh, and by prayer and fasting I want the Spirit of Christ in me and the Holy Spirit to fill the fasting, not by earthly bread alone but by the Bread of Life Himself, Then my fasting is no longer needed because the Bread of Life is sustaining me no matter how long I wait upon the answer to prayer, which is in Him.
This is not easy to do, and the disciples should have been in this frame of mind when they approached this kind of demon. Total and complete dependence upon The Christ and the Holy Spirit from the Father by whom we are sent.
Our prayers and fasting will not help, unless it is by the inflaming of the fast to bring upon our prayers the Power of God to do His work.
Does this sound like I don't believe in fasting?
But only God's way in this circumstance.
If we are ready to take on the Faith of the Son of God that is in us and by the Power of the Holy Spirit given and our faith now His faith, we are ready.
I must say all Christians are Satan proof by the Christ that is in them. In whom do we believe Christ or the Lie of satan.
Fasting until Christ comes for His Bride, In Christ; Phillip