Antony knows that his own life is in extreme danger because of his close relationship with Julius Caesar. His character does not suddenly change but just his manner of presenting himself. He pretends to be resigned to Caesar's death and shakes the bloody hands of the assassins, but it is strictly cunning and pretense. The practical-minded Cassius says:
I blame you not for praising Caesar so;
But what compact mean you to have with us?
Will you be pricked in number of our friends,
Or shall we on, and not depend on you?
To which Antony replies:
Therefore I took your hands, but was indeed
Swayed from the point by looking down on Caesaar.
Friends am I with you all, and love you all
Upon this hope, that you shall give me reasons
Why and wherein Caesar was dangerous.
And Antony continues:
And am, moreover, suitor that I may
Produce his body to the marketplace,
And in the pulpit, as becomes a friend,
Speak in the order of his funeral.
Antony is hiding his true feelings in the hope of saving his own life and, in addition, in the hope of receiving permission to speak in Caesar's funeral. It is all pure deception. Brutus is completely taken in, but Cassius, who is cunning, skeptical and worldly wise, is strongly opposed to letting Antony address the Roman mob. He intially wanted Antony murdered along with Caesar, but Brutus overruled him. And Brutus overrules him again when he says:
Brutus, a word with you.
You know not what you do. Do not consent
That Antony speak in his funeral.
Know you not how much the people may be moved
By that which he will utter?
Once Antony is alone with Caesar's body, having received permission from the noble but rather fatuous Brutus to make his funeral speech, Antony expresses the powerful, turbulent feelings he has been hiding. He begins by addressing his dead friend with two lines that clearly show he has been counterfeiting his true feelings of hatred and desire for revenge:
O pardon me, thou bleeding piece of earth,
That I am meek and gentle with these butchers.
He ends this soliloquy in the form of an address to the dead Caesar with one of Shakespeare's most ingenious metaphors:
That this foul deed shall smell above the earth,
With carrion men, groaning for burial.
Antony is an unusual character--a warrior and man of action who is also intelligent and articulate. He fully intends to make a speech that will arouse the people's pity and outrage and turn them against the conspirators. His sololiquy ostensibly addressed to Caesar's body not only reveals his true feelings but also shows his hitherto unrecognized and unappreciated eloquence, which will be fully displayed in the funeral oration. Prior to this speech to Caesar's body, the audience would have had no idea that Antony had the capacity for such brilliant rhetoric; but now they will be anticipating a funeral oration that will stir their own emotions as it does those of the Roman mob.