So, what do we know about this Macbeth character, anyways?
We know a wounded captain in the King's army says he is a fierce warrior. Macbeth's seeming valor has no trouble "unseaming" a foe, even one he knows personally,without so much as a handshake. Macbeth doesn't seem to be afraid of much, either. He shows little fear, welcoming fresh battle. For this he is rewarded by the King Duncan.
Think about these characteristics of Macbeth. How would you categorize him, knowing what you know from this third person description? Is he brave? Loyal? The epitome of a hero?
So now it's scene iii and Macbeth has only appeared via description and his name on the Globe Theatre Marquee.
And the first thing we see in scene iii are...Witches, with their evil rhyming couplets and ominous warnings. In walks Macbeth and his pal Banquo, fresh from battle. The witches make foreshadowing statements to Banquo & McB, which they don't understand.
But are they predictions? or are they planting a seed? Starting a thought? Building a mystery? Do the witches have any power other than the power of suggestion?
The idea that supernatural forces are at work in the play is probably why this play is so different from Shakespeare's other works. Since drama is a visual representation of literature, how would an objective correlative a la Eliot fit into this play?