The Lord is addressing his apostles. I therefore believe it is intended for those who have given up everything to follow Christ to be His disciple, to whom it applies; as well as moving mountains in the previous verse.
Mark 11:23 For verily I say unto you, That whosoever shall say unto this mountain, Be thou removed, and be thou cast into the sea; and shall not doubt in his heart, but shall believe that those things which he saith shall come to pass; he shall have whatsoever he saith.
Mark 11:23 For verily I say unto you, That whosoever shall say unto this mountain, Be thou removed, and be thou cast into the sea; and shall not doubt in his heart, but shall believe that those things which he saith shall come to pass; he shall have whatsoever he saith.
It is to those who have the faith of God or who have faith in God. Vs 22.
Jesus is simply telling Peter and those listening HOW he killed the fig tree.
If you look at what you quoted in vs 23 and compare that to what Jesus did with the tree, you might some striking similarities.
Vs 23 is what Jesus used to kill the tree. He did not ask God the Father to do anything.
He TOLD the tree what it was going to do, and it did it. He spoke to the tree like He said to do with the mountain.
If you don't doubt what you say shall come to pass, you will have whatsoever you say.
That is a spiritual law, forever established in heaven, because Jesus spoke or voiced it, and now it is written.
It will work for "whosoever" has faith in God or the faith of God.
But it will NOT work for those who are doubters, who call themselves believers, or those who fail to forgive others who offended them. As it is written in verses 25 and 26.