"Beware the ides of March" (Act I: Sc iii: Ln 18).This line is important because it's warning Caesar about what is coming. Caesar could take the warning but instead he ignores it. So he could've saved his life if he wasn't so confident.
Act IV: Sc iii
"Caesar must bleed for it an gentle friends let's kill him boldly not wrathfully" (Act II: Sc i: Ln 71). This line is important because it shows Brutus's reason for killing Caesar. If we didn't know the reason it would've seemed like he did it for no reason. Then his speech wouldn't make sense.
Act V: Sc iv
"Speak hand for me" (Act III: Sn i: Ln 78).This is the line that tells everyone to kill Caesar. Without this line no one would know when to and they would've attacked at different times. Then Caesar would've been able to stop them.
"To tell thou shall see me at Philippi" (Act IV: Sc iii: Ln 83). This line is telling Brutus that he is going to die in Philippi. Ghosts usually symbolize death. So Caesar saying he will see him again means he will die and see him.
"Thy life hath had some smatch of honor in it" (Act V: Sc iv: Ln 46). It's showing Brutus wanted to go out with his honor. Brutus and Cassius both were dying for Rome but Cassius did it more like a coward and had someone kill him. Brutus died by his own will making it honorable.
Keep your friends close and your enemies closer. If you keep your enemies close you can stop their plans before they happen. The conspirators all acted like Caesar's friend to close enough to kill him. If they hadn't the plan wouldn't of worked.