In response to religious leaders who challenged his authority, Jesus tells a story identifying them as rebellious vineyard workers. The vineyard is fruitful, but these managers refuse to offer the "owner" his rightful share. In other words, God's people want to worship him, but the established religious leaders garner the glory for themselves.
This also motivated their rejection of Jesus and his obvious divine authority. So, Jesus lets them know that he is the promised deliverer of God's people. He is the appointed leader of the Kingdom of God. Though the ones with positions of authority reject Jesus, he is God's choice, and God will soon make it clear that Jesus is the "cornerstone" for the entire Kingdom of God project that is underway.
When the cornerstone of a building is laid, the dimensions for the whole thing are determined. It is only a matter of the process of building. When the building is ready to be finished, the last thing is to set the capstone, locking everything else in place. As disciples in the Kingdom of God, we rejoice that the cornerstone is laid and the capstone is coming soon.