"O from this time forth / My thoughts be bloody, or be nothing worth"
This line represents the turning point of the play, when Hamlet finally decides to make his way back home and enact the revenge on Claudius. He is prompted to this decision because he sees all of the soldiers fighting for Fortinbras, and thinks that if they can fight for something that's not even personal, he should be able to fight to avenge his father's murder.
