In the context of the play, the phrase is a powerful moment that highlights the theme of friendship. Caesar's trust in Brutus is absolute, and he is completely shocked when Brutus turns on him. The betrayal is so great that Caesar can only utter the words "Et tu, Brute?" before he dies.
The phrase also highlights the fragility of friendship. Even the closest friendships can be broken by betrayal. This is a lesson that Caesar learns the hard way, and it is a lesson that the audience is left to ponder.
In addition to the theme of friendship, the phrase "Et tu, Brute?" also speaks to the theme of power. Caesar is a powerful man, but even he is not immune to betrayal. The phrase shows that even the most powerful people can be brought down by those they trust.
The phrase "Et tu, Brute?" is a powerful and memorable moment in Julius Caesar. It speaks to the themes of friendship, betrayal, and power, and it is a lesson that the audience is left to ponder long after the play has ended.