The disciples have asked Jesus how He was able to cause a fig tree to wither (Matthew 21:18–20). Jesus presents them with a lesson about the power behind faith, indicating that with faith they could have withered the tree, as well.
In fact, Jesus adds that with faith in God and without doubting, they could have the power to tell a mountain to be taken up and thrown into the sea. In part, this is an example of hyperbole: exaggeration for effect. At the same time, it’s good to remember that the power behind prayer comes from God, not the one who prays. If a request is aligned with God’s will, it’s not impossible for Him to accomplish it (Luke 1:37). At the same time, that means a person who is fully aligned with the will of God wouldn’t make requests He clearly does not want (Matthew 21:22; John 14:13–14).
The point, of course, isn’t that Jesus wants them to throw mountains into seas, including the Mount of Olives, which they are standing on. He wants the disciples to understand that, in and through Him, they will have power beyond themselves to accomplish what He gives them to do in the coming years.
Jesus fulfills a prophecy from Zechariah about the coming of the king to Jerusalem by riding in on a donkey. The people celebrate and praise Him as the Messiah. Jesus drives the marketers and moneychangers out of the temple and heals some people. He curses a fig tree and tells the disciples nothing will be impossible for them with faith. Jesus forces cowardly and hypocritical religious leaders to back down with a question about John the Baptist. He then exposes their fraudulent spirituality with two parables about vineyards. Jesus applies to Himself a psalm about a rejected stone being made the cornerstone by the Lord.