As a grain of mustard-seed - See the notes at Matthew 13:31-32. The mustard-seed was the smallest of all seeds. It has been supposed by some, therefore, that he meant to say, If you have the smallest or feeblest faith that is genuine, you can do all things. The mustard-seed produced the largest of all herbs. It has been supposed by others, therefore, to mean, If you have increasing, expanding, enlarged faith, growing and strengthening from small beginnings, you can perform the most difficult undertaking. There is a principle of vitality in the grain of seed stretching forward to great results, which illustrates the nature of faith. Your faith should be like that. This is probably the true meaning.

Ye shall say unto this mountain ... - Probably he pointed to a mountain near, to assure them that if they had such faith they might accomplish the most difficult undertakings - things that at first would appear impossible.

Because of your unbelief - Are we preachers of the Gospel? Do the things of God rest upon our minds with a deep and steady conviction? Can we expect that a doctrine which we do not, from conviction, credit ourselves, can be instrumental in our hands of begetting faith in others? So we preached, end so ye believed. The word preached generally begets in the people the same spirit which the preacher possesses. Instead of απιϚιαν, unbelief, the famous Vatican MS. and Cod. Cyprius, six others, Coptic, Ethiopic, Armenian, and Arabic, Origen, and Chrysostom, read ολιγοπιϚιαν, littleness of faith. The disciples had some faith, but not enough - they believed, but not fully.

As a grain of mustard seed - Some eminent critics think this a proverbial expression, intimating a Great Degree of faith, because removing mountains, which St. Paul, 1 Corinthians 13:2, attributes to All Faith; i.e. the greatest possible degree of faith, is attributed here, by our Lord, to that faith which is as a grain of mustard seed. However this may be, there can be no doubt that our Lord means, as Bishop Pearce well remarks, a thriving and increasing faith; which like the grain of mustard seed, from being the least of seeds, becomes the greatest of all herbs; even a tree in whose branches the fowls of the air take shelter. See Wakefield's Comment, and the note on Matthew 13:32 (note).

And Jesus said unto them, because of your unbelief,.... The Arabic and Ethiopic versions read, "because of your little faith", or "the smallness of your faith"; and so does one Greek manuscript; and which is what is doubtless meant by their unbelief; for they were not altogether destitute of faith, but their faith was very low, and their unbelief very great. Christ says, not because of the unbelief of the parent of the child, and those that were with him, though that also was a reason; but because of their unbelief, being willing to convince them of their unbelief, as he had done the father of the child, who had confessed it, and desired it might be removed from him: but lest they should think they had lost their power of doing miracles, Christ adds;

for verily I say unto you, if ye have faith as a grain of mustard seed; which was a very small seed, the least of all seeds, and is used very often proverbially by the Jews, to signify anything of a small quantity or weight (b), and is sometimes used of faith, as here; so speaking of the congregation of Edom, meaning the Christians, they (c) say,

"they have not , "faith as a grain of mustard seed".''

And it is used in like sense in other eastern nations; and by Mahomet in his Alcoran (d), who says,

"We will appoint just balances in the day of resurrection, neither shall any soul be injured at all, although the merit or guilt of an action be of the weight of "a grain of mustard seed".''

So that it has no reference to the quality of mustard seed, being hot and acrimonious; which has led some interpreters wrong, to compare faith unto it, for its liveliness and fervency: when our Lord only means, that if his apostles had ever so small a degree of faith in exercise, which might be compared for its smallness to this least of seeds, such an effect as he after mentions would follow; and which therefore is to be understood, not of an historical faith, by which men assent to all that is in the Bible as true; nor of a special, spiritual faith, by which souls believe in Christ, as their Saviour and Redeemer; for of neither of these can the following things in common be said; but of a faith of miracles, peculiar to certain persons in those early times, for certain reasons; which such as had but ever so small a degree of, as the apostles here spoken to might say, as Christ observes to them,

ye shall say to this mountain; pointing perhaps to that he was just come down from, which might be in sight of the house where he was,

remove hence to yonder place, and it shall remove: meaning, not that it would be ordinarily or ever done in a literal sense by the apostles, that they should remove mountains; but that they should be able to do things equally difficult, and as seemingly impossible, if they had but faith, when the glory of God, and the good of men, required it. So that it does not follow, because the apostles did not do it in a literal sense, therefore they could not, as the Jew insultingly says (e); since it was meant that they should, and besides, have done, things equally as great as this, and which is the sense of the words. So the apostle expresses the faith of miracles, by "removing mountains", 1 Corinthians 13:2 i.e. by doing things which are difficult, seem impossible to be done: wherefore Christ adds,

and nothing shall be impossible to you; you shall not only be able to perform such a wonderful action as this, were it necessary, but any, and everything else, that will make for the glory of God, the enlargement of my kingdom and interest, the confirmation of truth, and the good of mankind.

(b) T. Bab. Beracot, fol. 3l. 1. Megilla, fol. 28. 2. Nidda, fol. 66. 1. Maimon. lssure Biah, c. 11. sect. 4. Maacolot Asurot, c. 2. sect. 21. &c. 14. sect. 8. Tumaot Okelim, c. 4. sect. 2. & 7. 6. (c) Vet. Nizzachon, p. 148. (d) C. 21. p. 268. & c. 31. p. 336. Ed. Sale. (e) Vet. Nizzachon, p. 237.

Unbelief (ἀπιστίαν)

But the better reading is ὀλιγοπιστίαν, littleness of faith. Hence Rev., Because of your little faith.

And Jesus said unto them, Because of your unbelief: 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.

17:20 This mountain. Lofty Hermon, in plain sight.

Nothing shall be impossible unto you. Upon the condition of perfect faith. Compare Heb 11:1-40. Faith in Christ, faith exercised in fasting and prayer, are the conditions of power.

17:20 Because of your unbelief - Because in this particular they had not faith. If ye have faith as a grain of mustard seed - That is, the least measure of it. But it is certain, the faith which is here spoken of does not always imply saving faith. Many have had it who thereby cast out devils, and yet will at last have their portion with them. It is only a supernatural persuasion given a man, that God will work thus by him at that hour. Now, though I have all this faith so as to remove mountains, yet if I have not the faith which worketh by love, I am nothing. To remove mountains was a proverbial phrase among the Jews, and is still retained in their writings, to express a thing which is very difficult, and to appearance impossible. Matt 21:21; Luke 17:6.

17:14-21 The case of afflicted children should be presented to God by faithful and fervent prayer. Christ cured the child. Though the people were perverse, and Christ was provoked, yet care was taken of the child. When all other helps and succours fail, we are welcome to Christ, may trust in him, and in his power and goodness. See here an emblem of Christ's undertaking as our Redeemer. It encourages parents to bring children to Christ, whose souls are under Satan's power; he is able to heal them, and as willing as he is able. Not only bring them to Christ by prayer, but bring them to the word of Christ; to means by which Satan's strong-holds in the soul are beaten down. It is good for us to distrust ourselves and our own strength; but it is displeasing to Christ when we distrust any power derived from him, or granted by him. There was also something in the malady which rendered the cure difficult. The extraordinary power of Satan must not discourage our faith, but quicken us to more earnestness in praying to God for the increase of it. Do we wonder to see Satan's bodily possession of this young man from a child, when we see his spiritual possession of every son of Adam from the fall!