ESV - 20 He said to them, "Because of your little faith. For truly, I say to you, if you have faith like a grain of mustard seed, you will say to this mountain, 'Move from here to there,' and it will move, and nothing will be impossible for you.
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This is not an intended to be an answer to the question. However, I have used this to illustrate the issue. While at a regional conference of an association of independent churches in the Pacific Northwest several of us stayed with a local family. As we were being driven to the church one morning and broke over the crest of a steep hill we saw the beauty of the Snake River basin. Our driver shared with us that there had been a huge hill that blocked the view. He said that he had pray that the Lord would remove the blockage. It was not too long until his construction company received an invitation to bid on the removal of the hill and several months later, after winning the bid, God sent him to not only remove it, but also to make a profit and contributing to the financial needs of his construction crew.
The real blessing of God's promise that faith can move mountains is the the biggest mountains we face are not physical but are issues of sin we struggle with. Thank you, Lord.