Note how this scene is actually a kind of war in rhetoric, where both Brutus and then Marc Antony address the common people and try to persuade them of the truth of what they say. Note first of all that Brutus speaks in prose, presumably trying to speak at the level of the common people. He stresses his honour above all, repeating this twice before he begins his argument:
Belive me for mine honour, and have respect to mine honour, that you may believe.
The veracity of what he is about to say rests on his honour - the reputation that Brutus has as a noble Roman. Brutus protests that his love for Caesar was the same as any other man's love, but his greater love for Rome forced him to act:
Not that I loved Caesar less, but that I loved Rome more.
Thus Brutus explains his actions saying that it was for the good of Rome that he acted rather than any personal ambition, and that he loved Caesar just as much as the audience:
As Caesar loved me, I weep for him; as he was fortunate, I rejoice at it; as he was valiant, I honour him; but, as he was ambitious, I slew him. There is tears, for his love; joy, for his fortune; honour, for his valour; and death, for his ambition.
Notice here how Brutus is able to praise and remember Caesar for his greatness and good attributes without having to blacken his entire character. His appeal to the crowd at the end to effectively judge him clinches his argument, as as Marc Antony bears the body of Caesar forward, Brutus finishes his speech describing how he slew "my best lover for the good of Rome."