Antony's speech at Caesar's funeral is a masterpiece of rhetoric. He uses it to rally the people of Rome to his side against Brutus and the other conspirators who killed Caesar.
Brutus addresses the crowd just before Antony and endeavours to explain his reasons for killing Caesar. Brutus insists it was a matter of honour, that it was his duty to kill Caesar to prevent him becoming a tyrant and enslaving the people. Brutus's reasoning then is that killing Caesar was the honourable thing to do. The crowd are impressed with his passion, even if they don't really understand his explanation.
When Antony addresses the crowd, he skillfully undermines Brutus's speech without even appearing to do so. He never condemns Brutus directly, in fact he keeps on calling Brutus 'an honourable man' while at the same time contradicting Brutus' claims that Caesar was too ambitious and therefore had to be killed. He does this by citing instances of Caesar's generosity and compassion for the people, and also the time when Caesar refused to take a crown that was offered to him.
This repetition of the phrase, 'Brutus is an honourable man' is a clever rhetorical device. Antony is being wholly sarcastic when he says it. This has a cumulative impact on the crowd, as they listen to Antony demolishing all of Brutus's arguments. What Antony does, in effect, is to turn Brutus's own words against him.
Antony further enhances his appeal to the crowd with his claims to modesty:
I am no orator, as Brutus is,
But, as you know me all, a plain blunt man,
That love my friend (III.ii.218-220)
Antony thus denies that he has any skill of speech, comparing himself unfavourably to Brutus as an orator; yet his whole address demonstrates his mastery of verbal manipulation.