Brutus utters this line after he has run onto his own sword to kill himself. He would rather die than be captured by Antony and Octavius. With these final words, he is telling Caesar's spirit to rest easy, and remarking that he was actually much happier to take his own life than he was Caesar's. With this quote, Shakespeare is showing Brutus to be an honorable man, who chooses to die honorably. Antony reinforces this notion a few lines later, when, discovering Brutus's body, he says "This was the noblest Roman of them all."
Brutus says that he feels more justified in killing himself than he was in killing Caesar.
When Brutus walked in his garden in Act II as he attempted to reach a decision about what should be done about Caesar, he debated whether it would be better to rid Rome of a potential tyrant, or to let him rule and become cold and heartless in exercising his authority. Brutus decided Caesar should be prevented from ruling Rome because of Brutus's idealism and emotional state after reading the forged letters sent to persuade him to join the conspiracy.
As a result, in Act V, Scene 5, as Brutus recognizes defeat and prepares for death by his own sword so he will not suffer the ignominy of defeat, his final words indicate his remorse for his assassination of Julius Caesar. He states that what he is about to do is much more honorable than his act of stabbing Caesar, an act which resulted in civil discord in Rome and conditions much worse than they would have been had Caesar lived and become emperor.
Unlike Caesar's death, in which others such as Marc Antony gained honor, no one can take honor from the suicide of Brutus. Antony acknowledges that Brutus was "the noblest Roman of them all" (Act V, Scene 5, line 68) because he was the only one who did not kill Caesar out of envy, but in a "general honest thought/and common good to all" (Act V, Scene 5, lines 72-73).