Pathetic fallacy - tempestuous weather creates an ominous feel to the audience.
Foreshadows he violence that will ensue later on in the play.
"No man born of woman shall harm Macbeth" ↝ [a4s1]
Each prophecies are equivocal and cryptic. Although they're giving Macbeth an important insight to his safety, they're only giving him an ephemeral sense of security and invincibility.
"Fair is foul and foul is fair" ↝ [a1s1]
Oxymoronic language creates a sense of confusion showing us that the witches are not be trusted.
The speech is conflicting and doesn't correlate with reality which highlights the hypocrisy the characters will adopt to conceal their intentions.
Macbeth calls the witches "imperfect speakers" ↝ [a1s3]
Their words are vague & ambiguous as they're not a source of control but a source of temptation.
The witches speak in riddles that are meant to be misunderstood but Macbeth chooses to ignore this as his greed for power overcomes him. Therefore, it could be argued that they're not controlling fate, rather they're allowing Macbeth to gain validation of the desires he already had.
