"O you hard hearts, you cruel men of Rome,Knew you not Pompey?"
"I have heard Where many of the best respect in Rome, Except immortal Caesar, speaking of Brutus And groaning underneath this age's yoke"
"Be you content. Good Cinna, take this paper, And look you lay it in the Praetor’s chair, Where Brutus may but find it;"
This quote introduces us to the idea that not all citizens want Cesar as their ruler. His leadership has given rise to concern in Rome. After defeating Pompey, some citizens quickly supported Cesar while others oppose him. Many towns people are celebrating his victory and return to Rome while others remain spiteful.
The conflict of the story is being introduced here. Cassius wants to remove Cesar from power. He also wants Brutus on his side. Cassius is trying to manipulate Brutus into believing the people think very highly of him. We get to see Cassius as an antagonist to Cesar and learn his intentions.
The next focus of the plot is revealed here. Cassius plans to have Cinna plant fake letters around Rome in places where Brutus will see them. These letters will express desire for Brutus to be in power. Cassius plans to use this to manipulate Brutus into supporting his side.