as the witches are aware that Macbeths ambition and hubris is his hamartia, they are duplicitous in using that to lure him into the idea of committing regicide
"All hail Macbeth, that shall be king hereafter !"
Shakespeare utilises the theme of the supernatural, personified through the witches, to illuminate the fatal consequences of being involved with the forces of evil
Macbeths relationship with the witches is microcosmic of why we should not be involved with the supernatural because of its fatalconsequences which is down fall
"though his bark cannot be lost, yet it shall be tempest-tossed"
Macbeth is a puppet to the witches
"so foul and fair a day I have not seen"
"harpies"-they are the ministers of the thunder, Zeus
"your face my thane is like a book"
"imperfect speakers"
ostensible
seemingly true but not necessarily
"look not like the inhabitants of the earth and yet are on it"
less syllable =less power
the trochaic tetrameter also shows the witches social exclusion- maybe to make us feel bad for them and sheds light on why they trick men perhaps because they do not have husbands themselves - or simply because its a patriarchal society - even doubly marginalised because they are not only poor("rags") but also ugly ("beards")
the childish portrayal of the witches is further reinforced as a recent royal Shakespeare company production cast three primary school aged girls to play the witches() yes you can talk about modern day interpretations as part of your context ho)
Alternative interpretations
Shakespeare does not believe in witches at all and although they do cast a few "charms" they never actually control the weather and instead the "thunder..." is simply a way of seeing further into the future of perhaps what is going happen to Macbeth- which subtly mocks/undermines the king's rather foolish belief in witchcraft as he believed that witches tampered with the weather while he was on ship
The witches also never point out any instructions for Macbeth to kill Duncan or Macduff's family and its only his idea- showing how the witches aren't evil themselves but simply help to bring out the evil in others
they speak in trochaic tetrameter- its the opposite of iambic- distinct them from rest of the characters- but it doesn't make them sound sinister but rather silly and childlike-that is how nursery rhymes sounded -mocking the belief in witchcraft and subtly highlighting that a belief in witchcraft is also just as childish
a patriarchal society creates witches as they're not given power in the real world they have to get it from the devil