Stephen gives a summary of the history of Israel at his trial. It demonstrates that he is a good Jew who listened to all his lessons at synagogue. However, he uses that history to remind his fellow Jews that they have a habit of disobeying God and not listening when God sends prophets to try to correct them. He lets them know they are doing that now by rejecting Jesus and His followers. Stephen is executed by a hysterical mob for his boldness in telling the people what they needed to hear. Luke also introduces Saul, who will play a major role in the rest of the story.
Doing what God wants and speaking on His behalf does not always lead to an easy life. We would like for everything to turn out well when we obey God, but God may have different plans. The story does have a happy ending with Jesus standing to welcome Stephen to heaven. We have a similar ending waiting for us.