Supernatural Forces and Corruption
The witches' opening paradox "fair is foul, and foul is fair" establishes how supernatural forces corrupt natural order. This double meaning suggests that nothing in the play will be as it seems - good will become evil, and evil will appear attractive.
Banquo's observation about the witches having "beards" yet appearing to be women emphasises their unnatural appearance. In Jacobean belief, physical appearance reflected inner character, so their strange looks expose their evil nature.
Lady Macbeth's plea to "unsex me here" connects her to supernatural power traditionally associated with witches. Her desire to abandon feminine nature and embrace masculine violence would have shocked contemporary audiences.
Historical Context: King James I wrote 'Daemonology' about witches, so Shakespeare was tapping into real social anxieties about supernatural corruption and the devil's influence.
The supernatural elements don't just add spooky atmosphere - they represent the external temptations that prey on existing human weaknesses. The witches don't force Macbeth to act; they simply reveal and amplify what's already lurking in his heart.