Early Ambition and Deception
"Fair is foul and foul is fair" sets the tone for the entire play - nothing is what it seems in Macbeth's world. The witches speak these words in Act 1, Scene 1, warning us that appearances can't be trusted throughout the tragedy.
When Macbeth says "Stars, hide your fires, let not light see my black and deep desires" in Act 1, Scene 4, he's already plotting Duncan's murder. He doesn't want God (represented by light) to see his evil thoughts, showing how ambition is already corrupting his morality.
Lady Macbeth reveals Macbeth's true nature when she worries he's "too full o' th' milk of human kindness" in Act 1, Scene 5. She sees his natural compassion as weakness rather than strength - a complete reversal of normal values.
Top Tip: These early quotes show how the play's central themes of ambition versus morality are established right from the start.