What does Mark 11:22 mean?

In Mark, Peter merely mentions that the tree has withered (Mark 11:21). In Matthew, the disciples ask how (Matthew 21:20). Jesus has shown authority over illness, injury, demons, death, nature, food replication, and even one coin-hungry fish (Mark 5:1–20; 6:30–44; 6:53–56; Matthew 17:24–27). The disciples perform many of these miracles as well (Mark 3:13–21). No other miracle, however, is recorded of Jesus specifically affecting plant life.

It's possible that Jesus destroys the tree as a symbol of the coming destruction of Israel. The Old Testament often compares Israel to a fig tree, associating the ruin of its fruit with God's judgment (Jeremiah 8:13; Hosea 9:10; Micah 7:1–7). Jesus knows that Israel and Judaism have no more fruit to give the world. They will reject and kill Jesus when they should welcome Him as God's Messiah. In AD 70, Jerusalem will be destroyed and the Jews scattered, unable to return as a sovereign nation until 1948.

But Jesus also knows the disciples can't always handle the bigger picture. When He walks on the Sea of Galilee in a display of His glory and authority over nature, the disciples completely misinterpret what is happening and think He's a ghost. Instead of teaching them about this wonderous new revelation of who He is and what He can do, Jesus has to calm their fears (Mark 6:45–52). Similarly, when Jesus is using a metaphor of leaven to represent the false teachings of the Pharisees and Herod, the disciples think He is scolding them because they forgot bread (Mark 8:14–21).

So, if Jesus' point is that Israel has lost its usefulness and will be destroyed, it's a message the disciples aren't ready for, yet. Instead, Jesus teaches them a more basic skill that will get them through any hardship: faith in God. The two are related. The Jewish Christ-followers will need all the faith they can get when Jerusalem is destroyed.