Mark 11:23 (KJV)  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.

This is the exhortation of Christ in Mark 11:22 (KJV) And Jesus answering saith unto them, Have faith in God.

Christ also attested to what God can do for His people where no man can. And so Jesus gives this very hard thing that God can do to jolt His people to have faith in God.

Truly, with God all things are possible. Let His people not doubt what God can and will do for them as He promised in His Word. Amen.