What does Matthew 21:45 mean?

This conversation began when some chief priests and elders approached Jesus with a question about the source of His authority (Matthew 21:23). Now Matthew shows that some Pharisees were present, as well—at least they had arrived by the time Jesus finished these two parables.

Instead of finding ammunition to use against Jesus, though, He had forced them to back down since they were unwilling to publicly say that John the Baptist was not sent from God (Matthew 21:25–27). Jesus launched from this into two parables that thoroughly condemned these Jewish religious leaders. He had indirectly owned His own role as the Son of God, predicting both His own death and God's coming judgment of these Israelite leaders (Matthew 21:28–41).

Now Matthew adds a note to let his readers know that the chief priests and Pharisees understood that Jesus was talking about them all along. They grasped that He was condemning them and predicting that the kingdom would be taken from them. It's not surprising that they were looking for a way to arrest Jesus and stop Him from teaching these things.