Jesus said (Matthew 17:20)
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.”
Jesus is emphasising the importance and power of faith more than the need to rearrange the landscape. He is saying that faith is so extraordinarily powerful that seemingly impossible things become possible when we ask God in faith. As James said
The prayer of a righteous person has great power as it is working. (James 5:16).
Of course, there are conditions on our requests to God being fulfilled. One of them is given in 1 John 5:14:
And this is the confidence that we have toward him, that if we ask anything according to his will he hears us.
So our requests have to be consistent with God’s will. Perhaps moving a literal mountain might occasionally be according to God’s will. But I think Jesus was talking about seemingly insurmountable problems that face us. If we pray in faith for God to remove such a “mountain”, and it is according to his will, then it will happen!
For more thoughts on prayer, see Chapter 9 from The Way of Life.