What does Luke 9:21 mean?
Jesus' identity has been in question from the moment Joseph first learned Mary was pregnant (Matthew 1:18–25). Since the beginning of His ministry, it has only grown. The religious leaders want to know why He has the audacity to forgive sins (Luke 5:20–21; 7:49). The disciples want to know who can calm a raging sea or walk on water (Matthew 8:27; Luke 8:25; John 6:16–21). The people think He marks the return of the prophets of old—maybe even Elijah, himself—while Herod Antipas wonders if He is John the Baptist, raised from the dead (Luke 9:7–9; Mark 6:14–16).Peter speaks for the disciples by declaring Jesus is "The Christ of God" (Luke 9:20), a statement Jesus says is an inspired word which will be the foundation of His church (Matthew 16:17–18).
This is the first of two times in this chapter where Jesus tells the disciples not to reveal something about Him. The second is after the transfiguration when Jesus tells Peter, James, and John to keep secret the vision of His glory until after the resurrection (Luke 9:28-36; Matthew 17:9). Several times, Jesus silences demons who compulsively identify Him as the Son of God (Mark 3:11–12).
The people were not ready for this information, yet. God works carefully through history, interacting with people, nations, and cultures to fulfill His plans and promises. Over-zealous followers, having seen how Jesus can provide food, already attempted to make Jesus king by force (John 6:15). The disciples think He is the prophet Moses promised and will win Israel political independence (Deuteronomy 18:15). They don't understand there is much that must happen first (Acts 1:6–7).
Jesus will face a cross before He takes His throne; His disciples need to be willing to follow His example (Luke 9:22–27). They will see miraculous things that affirm Peter's words (Luke 9:28–36), but their faith is still weak (Luke 9:39–40). They are thinking of the glory Jesus will give them (Luke 9:46–56), but before they receive His glory, they need to learn to sacrifice their loyalty to their earthly lives.