How did the people of Israel treat the prophets God sent to them?
The people of Israel killed the prophets God sent to them, or at best threw them into a dungeon, and they refused to hear them. Although God sent these prophets to His covenant people, they rejected and murdered them; God did not cancel the nation but later sent His Son.
Les explains that when God called the nation of Israel out, gave them the covenant promises, and called them His Son and favored nation, He dealt with them through the Old Testament years by sending the prophets. The people killed those prophets, or at best threw them in the dungeon, and refused to hear them. Yet God did not cancel the nation of Israel because of that. Instead, He next sent His Son. In the parable context, the chief priests and Pharisees understood that Jesus was pointing the finger at them.