Matthew 17:19-20

Then came the disciples to Jesus Namely, the nine disciples, who had been left with the multitude, when Jesus and the three others went up to the mount. They were silent before the multitude, ashamed, it seems, that they could not cast out this evil spirit, and, perhaps, vexed lest through some fault of their own they had lost the power of working miracles, formerly conferred upon them. But when they came with Jesus to their lodging, they asked the reason why they could not cast out that particular demon? Jesus said, Because of your unbelief Because in this particular you had not faith. You doubted whether I could or would enable you to cast out this evil spirit, and I permitted him to resist your efforts, to reprove the weakness of your faith. For if ye have faith as a grain of mustard-seed If ye have the least measure of the faith of miracles; ye shall say to this mountain, Remove, &c. Ye shall, by that faith, be able to accomplish the most difficult things in all cases wherein the glory of God and the good of his church are concerned. It is certain that the faith here spoken of may subsist without saving faith: Judas had it, and so had many, 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 by him in an extraordinary and supernatural way, at that hour. Now, though I have all this faith, so as to remove mountains, yet if I have not the faith that 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.