Lately I have been meditating on Matthew 17:19-20.
19 Then the disciples came to Jesus privately and said, “Why could we not drive it out?” 20 And He *said to them, “Because of the littleness of your faith; for truly I say to you, if you have faith [b]the size of a mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move; and nothing will be impossible to you. 21 [[c]But this kind does not go out except by prayer and fasting.”]
Joseph Prince and others have addressed this in a newsletter that was published on another blog. Here is the link.