In the last scene of the play Antony pays this tribute to the man he deceived and subsequently defeated in battle:
This was the noblest Roman of them all:
All the conspirators save only he
Did that they did in envy of great Caesar;
He only, in a general honest thought
And common good to all, made one of them.
His life was gentle, and the elements
So mix'd in him that Nature might stand up
And say to all the world 'This was a man!'
Cassius was extremely anxious to draw Brutus into the assassination plot. Without Brutus the others might never have acted against Caesar because they were all afraid of the Roman people and even afraid of Caesar himself. Brutus had such a reputation for integrity and patriotism that his name was sufficient to draw men into the conspiracy and to give that conspiracy the kind of creibility it needed. Even so, it was fairly easy for Antony to turn the plebians against the conspirators by reminding them of their former love for Caesar, of everything he had done for them, and everything he might have done if he had remained alive. All Antony needed was permission to speak at Caesar's funeral.
People tend to judge others by themselves. Cassius didn't trust Antony because he judged him to be as cunning and selfish as himself. Brutus trusted Antony because he believed in his pretense of good will. Brutus desperately wanted everyone to believe that he acted for unselfish reasons, and he wanted to trust Antony because Antony appeared so willing to listen to him, understand his motives, forgive him, and join him in establishing a new democratic government.
Throughout the play, Brutus acts honorably. He does a great deal of soul-searching before he decides to join Cassius in the plot. Shakespeare brings this out in Brutus' long soliloquy in Act 2, Scene 1, which begins with the following lines:
It must be by his death: and for my part,
I know no personal cause to spurn at him,
But for the general. He would be crown'd:
How that might change his nature, there's the question.
It is the bright day that brings forth the adder;
And that craves wary walking.
Throughout this soliloquy he does not once mention any personal motive for wanting Caesar dead. He knows "no personal cause to spurn at him." On the contrary, he is a good friend of Caesar and could probably be even better off in all respects if Caesar became king. As Cassius observes in Act 1, Scene 2:
Well, Brutus, thou art noble; yet, I see,
Thy honourable metal may be wrought
From that it is disposed: therefore it is meet
That noble minds keep ever with their likes;
For who so firm that cannot be seduced?
Caesar doth bear me hard; but he loves Brutus:
If I were Brutus now and he were Cassius,
He should not humour me.
Instead of gaining anything by the assassination, Brutus ends up losing everything, including his beloved wife Portia, who commits suicide when she realizes that her husband and his followers are doomed.
What makes Brutus noble, apparently, is that he is a scholar and a solitary philosopher. This makes him unworldly, and it is his unworldliness that allows him to be manipulated by Cassius and deceived by Antony, both of whom are merely cunning and not exceptionally intelligent men.
Cunning is but the low mimic of wisdom.