Matthew 21:12 This is the second time Jesus cleared the temple (John 2:13-17). Merchants and money-changers set up their booths in the court of the Gentiles in the temple, crowding out the Gentiles who had come from all over the civilized world to worship God. The merchants sold sacrificial animals at high prices, taking advantage of those who had come long distances. The money changers exchanged all international currency for the special temple coins - the only money the merchants would accept. They often deceived foreigners who didn't know the exchange rates. Their commercialism in God's house frustrate people's attempts at worship. This, of course, greatly angered Jesus. Any practice that interferes with worshiping God should be stopped.
Matthew 21:19 Why did Jesus curse the fig tree? This was not a thoughtless, angry act, but an acted-out parable. Jesus was showing His anger at religion without substance. Just as the fig tree looked good from a distance but was fruitless on close examination, so the temple looked impressive at first glance, but its sacrifices and other activities were hollow because they were not done to worship God sincerely. If you only appear to have faith without putting it to work in your life, you are like the fig tree that withered and died because it bore no fruit. Genuine faith means bearing fruit for God's kingdom.
Matthew 21:21 Many have wondered about Jesus' statement that if we have faith and don't doubt, we can move mountains. Jesus, of course, was not suggesting that His followers use prayer as "magic" and perform capricious "mountain-moving" acts. Instead, He was making a strong point about disciples (and our) lack of faith. What kinds of mountains do you face? Have you talked to God about them? How strong is your faith?
Matthew 21:22 This verse is not a guarantee that we can get anything we want simply by asking Jesus and believing. God does not grant requests that would hurt us or others or that would violate His own nature or will. Jesus' statement is not a blank check. To be fulfilled, our requests must be in harmony with the principles of God's kingdom. The stronger our belief, the more likely our prayers will be in line with God's will, and then God will be happy to grant them.