Lets read the entire passage shall we?
20 Now in the morning, as they passed by, they saw the fig tree dried up from the roots. 21 And Peter, remembering, said to Him, “Rabbi, look! The fig tree which You cursed has withered away.”
22 So Jesus answered and said to them, “Have faith in God. 23 For assuredly, I say to you, whoever says to this mountain, ‘Be removed and be cast into the sea,’ and does not doubt in his heart, but believes that those things he says will be done, he will have whatever he says.24 Therefore I say to you, whatever things you ask when you pray, believe that you receive them, and you will have them.
Do you know of any case where a mountain has been moved out of it's place and cast into a sea simply by asking? I will answer for you, NO. So it is safe to say that Jesus was using hyperbole to make His point. In another case Jesus said that we only need a bit of faith as a mustard seed. The moral of this story is "faith in the heart with no doubt" and you will move mountains in the New Kingdom not here on this earth.
