Jesus is now in the final days before His crucifixion. He knows His time is coming very soon and careful navigation of the opposition in order to ensure His rejection doesn't come prematurely is now set aside. He becomes increasingly direct and aggressive with the Scribes and Pharisees and Chief Priests.
He begins with a parable about a king who prepares a wedding feast for his son. The message is unmistakable. Israel was the chosen guest, invited and waited on by the King for their arrival. But they never show up. They show one sign of rejection after another and the King eventually turns his attention to the rest of the world and extends the invitation to the nations.
And in the middle of this parable, Jesus inserts a theological gem. One man arrives without wedding clothes and is thrown out. The invitation is freely given, but entrance requires righteousness. We cannot stand before a Holy and perfect God in our own righteousness. Isaiah makes it clear that all our righteous deeds are like a filthy garment to the Lord (Isaiah 64:6). And Paul in Galatians makes it clear that we clothe ourselves with Christ (Galatians 3:27). And in this parable, Jesus makes it clear that we need the righteousness of Christ.
The Jewish leaders continue to press Jesus, attempting to trap Him with political questions about the Jew's obligation toward their oppressive Roman leaders like Caesar, questions about divorce and the resurrection, and questions about the greatest commandment. Each time, He exposes their shallow understanding. They are familiar with the scriptures, but they fail to see God revealed in them.
The last correction Jesus offers them is a full understanding of the Messiah. That the Messiah is not merely David's son, but David's Lord. They were looking for a political deliverer and an earthly conquerer, but the true King of Israel stood before them with a far deeper and a far more everlasting deliverance.