Matthew 17:20

“And Jesus said unto them, because of your unbelief, etc.] 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…”

“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…”

“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…”

“17:20 Here, the expression don’t have enough faith is virtually synonymous with no faith. • faith even as small as a mustard seed: This could mean that if the disciples had even very little faith they would be able to accomplish great things (21:21; cp. 1 Cor 13:2). It could also mean that if they would allow their faith to grow (see Matt 13:31-32), they could act with courageous belief. • Moving mountains is an adage for overcoming obstacles and fulfilling God’s purposes (Isa 40:4; 49:11; 54:10; 1 Cor 13:2).”

“Because: Mat 17:17, Mat 14:30, Mat 14:31; Heb 3:19 If: Mat 21:21; Mar 11:23; Luk 17:6; Co1 12:9, Co1 13:2 faith: That is, as Bp. Pearce well remarks, a thriving and increasing faith, like a grain of mustard seed, which, from being the least of seeds, becomes the greatest of all herbs. a grain: Mat 13:31; Mar 4:31 nothing: Mar 9:23; Luk 1:37, Luk 18:27 Matthew 17:21”