The Witches are the first characters we are introduced to in the play. Shakespeare couples their introduction with pathetic fallacy, enrobed in "thunder and lightning", making the atmosphere volatile and ominous. It could be argued that Shakespeare opens the play in media res, meaning it is in the midst of the plot, as it seems the Witches' conversation is drawing to a close - "when shall we three meet again?". This immediately establishes a sense of mystery and secrecy.
Witches' in Act 1 Scene 3
In act one scene 3, Macbeth and Banquo meet the Witches for the first time. Banquo perceives their overt evil and dehumanises them in his description "look not like the inhabitants of the earth". The witches' physiognomy (appearances reflective of your character) exposes them as inhumane and evil. Banquo is portrayed as perceptive, as it was believed he was an ancestor of James I - thus this is a form of indirect flattery.
Witches and masculinity
The Witches also have "beards" throughout the text - Masculinity is synonymous with power, thus this description imbues them with a threatening dominance.
Witches' speech - Trochaic tetrameter
They speak in trochaic tetrameter, which is distinct from the iambic pentameter that noble characters speak in throughout the play - this gives their speech an eerie, songlike quality. This is reinforced when Banquo later refers to them as "instruments of darkness", suggesting their evil musicality, perhaps showing how their words are almost hypnotic for Macbeth.
Witches' speech - Rhyming Couplets
It is notable they have an unnatural manner of speech. This is reinforced through their use of rhyming couplets. The rhyming couplets make it sinister, almost like a dark nursery rhyme or spell.
Witches' speech - Paradoxes and oxymorons
This is seen when they chant the paradoxical phrase "fair is foul and foul is fair", which foreshadows the overarching theme of appearance vs reality which endures throughout the rest of the play. The frictive 'f' sound is menacing, and Shakespeare uses a confounding example of epanados (when a phrase at the start is repeated/expanded at the end) to set up an oxymoron which conveys the ambiguity of their prophecies. Their conflicting language is notable throughout the entirety of the play, reinforcing their deceitful and duplicitous intentions.
Witches' influence over Macbeth
Macbeth's first line in the play echoes the paradoxical language of the witches: "so foul and fair a day I have not seen". The oxymoron 'foul' and 'fair' directly mirrors the Witches ominous nursery rhyme like chant - Macbeth is instantly introduced as malleable and susceptible to their malevolent schemes. The lexis (word choice) on "not seen" implies blindness or a loss of vision. This could parallel how Macbeth is blinded by their equivocal prophecies, leading to him to lose sight of reality. It foreshadows how Macbeth will be forever entranced by evil.
Witches' influence over Macbeth 2
His words emulate that of the witches before their first interaction, alluding to how he has an innate sense of unchecked evil he is unable to control.
Summary
The play begins in mediares within a meeting of the witches. This immediately sets a tone of unease as it immerses the audience within the supernatural. For Shakespeare's contemporaries, this would elicit a fearful sense of intrigue and set the play into motion.
The Witches are presented as inhumane and instruments of evil. Their cadence of speech, paired with the archetypical presentation of them, is reflective of their deceitful and duplicitous nature.
Summary 2
Macbeth is presented as submissive to the malevolent entity of the Witches. He is instantly presented as malleable to their treacherous schemes - foreshadowing his downfall will be synonymous with his interference with the supernatural.