In Act 1, Scene 1, Flavius and Murellas are yelling at random people in the street who were celebrating Caesars victory. Flavius said, "Hence! Home, you idle creatures get you home! Is this a holiday?" (1;1;1-2)which was important because it introduced us to what was happening in the story.
Act IV: Sc III
In Act 2, Scene 1, Brutus is contemplating what Cassius has said to him, saying "It must be by his death, and for my part I know no personal cause to spurn at him. But for the general. He would be crowned. How that might change his nature, there’s the question." (2;1;10-14) and that's important because we see how Brutus is slowly changing his mind.
Act V: Sc I
In Act III, Scene I, we see Antony speaking to Caesar's corpse, curing the men who killed him by saying "Woe to the hand that shed this costly blood!" (3;1;273)
THEME Act : Sc
In this scene, the ghost of Caesar appears in front of Brutus to tell him he's going to die at Phillippi, saying :"To tell thee thou shalt see me at Philippi." This is important because now we know that Brutus will not survive.
In Act V, Scene I, Cassius is having a heart to heart with Brutus, saying "The very last time we shall speak together.What are you then determinèd to do?" This is importsnt because we get to see an entirely new side to Cassius
In Act IV, Scene IV, Antony speaks of Brutus kindly after his death, saying "This was the noblest Roman of them all." This scene is also important because we learn that even Brutus's enemies respected him.