The Soothsayer tells Caesar in this scene, to beware the ides of March. Being arrogant like Caesar himself, he decides to not believe the Soothsayer's wise advise. He claims that Rome is more important than his own well-being while he continues to go about his business. "Beware the ides of March!" (1:2)
Act 4, Scene 3
Brutus joins the conspirators after much convincing. He takes charge in a way and becomes leader. He veto's the preposition of swearing to an oath, because they should be honest all of the time without the encouragement of an oath. "No, not an oath. If not the fare of men, the sufferance of our souls, the time's abuse..." (2:1)
Act 5, Scene 5
Due to his arrogance, Ceasar avoids the Soothsayer's advice and warnings and is killed by the conspirators. If he listened and took the wise advise of the Soothsayer, his life would have been spared. "Et tu, Brute? Then fall Caesar!" (3:1)
Caesar's ghost visit Brutus as he tries to sleep. His ghost tells Brutus that he shall see him in Philippi. This is foreshadowing that Ceasar will die in Philippi and they'll lose the war. As he awakens he asks the other men if they too saw the ghost. No one but him saw it. He then makes the decision to start the march. "To tell thee thou shall see me at Philippi" (4:3)
Brutus kills himself because he comes to the realization that they've lost the battle. He asks tree men to assist him in this suicide, none of which agree to. The fourth man he asks is an old school friend, who says he'll help Caesar out of respect. "Farewell, good Strato- Caesar, now be still; I killed not thee with half so good at will" (5:5)
The theme of the play is that keeping your promises earns you more respect than lying to become powerful will. Brutus killed himself because he got defeated and he said he would end his life if it would if Rome's well-being relied on it. For this, he was properly buried. "This was the noblest Roman of them all. All the conspirators save only he did that. "