What does Luke 20:17 mean?

This establishes the moral of the parable of the wicked tenants (Luke 20:9–16). In the story, a landowner hired workers to care for his vineyard. When he sent his son to collect some of the grapes, the tenants killed him, thinking they would now inherit the land. In the same way, God has established religious, legal, and civil leaders to ensure the people properly worship Him and live according to His ways. Now, He has sent His Son. Those leaders will kill His Son to keep control over the people: religiously, legally, and civilly.

After the tenants kill the son, the landowner returns, destroys the tenants, and finds new farmers for his vineyard. About less than forty years after the Jewish leaders kill Jesus, God allows the Romans to destroy the temple and Jerusalem and send the surviving priests and scribes into exile.

Jesus doesn't give specifics, but the people can't understand how God could take the Jewish leaders out of power. Jesus explains that it's because of Him. He is the cornerstone of God's kingdom. God's kingdom is built on Him. The Jewish leaders can reject Him all they want, but it makes no difference. He quotes Psalm 118:22. The stanza talks about how the righteous will enter the gate of Yahweh, that God is their salvation, it is His doing only, it is marvelous and worthy of rejoicing (Psalm 118:19–24).

The Jewish leaders may kill the Son, but that doesn't stop God's plan. He is the foundation of a new manifestation of God's people: the church (1 Corinthians 3:11; Ephesians 2:20).