What does Jesus' parable illustrate about God's dealings with Israel in the Old Testament?
The parable illustrates that God the Father sent prophets to His covenant nation Israel throughout the Old Testament, but they killed them, imprisoned them, and refused to hear them. Yet God did not cancel Israel; He next sent His Son.
Les explains that when God called Israel out, gave them the covenant promises, called them His Son and His favored nation, He dealt with them through the Old Testament years by sending the prophets. But they killed the prophets, or at best threw them in the dungeon, and refused to hear them. Even so, God did not cancel the nation of Israel. He next sent His Son, and the chief priests and Pharisees understood that He was pointing the finger at them.