The play is a warning about unchecked ambition. Macbeth and Lady Macbeth's desire for power overrides every moral constraint until it destroys them both. Shakespeare presents ambition as potentially the most dangerous human quality.
'Fair is foul and foul is fair.' Nothing in Macbeth is what it seems: the witches appear wise but deceive; Lady Macbeth appears a devoted host but is plotting murder; Macbeth appears a loyal subject but plans regicide.
Shakespeare explores how guilt works on the human mind. Both Macbeth (the hallucinated dagger, Banquo's ghost) and Lady Macbeth (the sleepwalking, the invisible blood) are driven to madness by their own consciences. Guilt, in Macbeth, cannot be escaped.
The witches' prophecies raise a fundamental question: is Macbeth's fate determined, or does he freely choose evil? Shakespeare leaves this deliberately unresolved. The witches predict but never force. Macbeth chooses.
The murder of a king is presented as a disruption of natural and divine order. Scotland descends into tyranny and violence. Order is only restored when the rightful heir Malcolm is crowned.