What is the role of the three witches in Shakespeare's tragic play Macbeth?
In addition to what's been written above, the witches in Shakespeare's Macbeth contribute to the theme of equivocation present in the play.
They are the master equivocators. They tell Macbeth predictions that seem fool proof, but in fact are not. Who could guess that soldiers would camouflage themselves with branches and leaves so that when they move in toward Macbeth's castle they, from a distance, look like trees moving? Who could guess that Macduff's mother died in child birth before Macduff was born, so that he actually wasn't born of woman, but born of a "body."
The Macbeths equivocate, in a sense, when they behave so hospitably toward Duncan then assassinate him. Macbeth equivocates when he tells Banquo they will talk the next day, knowing that the murderers will kill Banquo later that day. Malcolom suspects Macduff of equivocation when Macduff comes to England to join Malcolm in the fight against Macbeth.
Further, this theme is emphasized by the porter in the famous comic relief scene that separates Duncan's slaying from the discovery of his body.
Again, the witches are the masters of equivocation. Macbeth is quite an equivocator himself, but the witches are certainly one up on him.
The three witches, or Weird Sisters, were used to appeal to those interest in the occult, which many people in court were, especially King James. So while Shakespeare used this as a way to please the royalty and people that were paying him for his works, they also function as a way to drive the plot and create tension within the viewer. They drive the plot because they foreshadow/foretell the future action of the play. When Macbeth is unhappy and fears Banquo, he goes back to them as a source of knowledge. However they also create tension because the classic question arises: Is it their fault of telling Macbeth this prophecy (which may or may not have actually come true) or is it Macbeth's own greed and ambition that destroys him? So they are essential to the ideas of fate and occult within the play.
In the play 'Macbeth' by William Shakespeare, one of the main roles of the three witches is to cast a general aura of mystique, magic and menace over the entire play right from the start. Different critics have different ideas as to why this is. Some are concerned with the alleged interset of King James in witchcraft - apparently there were things in his background which made him superstitious so you may want to check this out. Also, critics have explored the area of genderless beings - these 'creatures' were supposed to make people feel 'afeard' as one could not be sure what they were (note Lady macbeth's request to 'unsex me' too in connection with this and check out too.)
The witches have a great role in influencing the decision and actions of Macbeth.In the opening scene,the witches say,'fair is foul and foul is fair'.In the next scene,while Macbeth is returning from the battle-field,he also says,'So foul and fair a day i have not seen'.The common phraseology between the two is unmistakable.There seems to be some sort of spiritual link between Macbeth and evil.
The witches flare up the ambitious nature of Macbeth.they make prophecies and address him as the 'Thane of Glamis' and the 'Thane of Cawdor'.They also predict that he shall be the king afterwards.Just as he comes to know that the king has conferred upon him the title,he starts thinking about other prophecy.It shows how the words of witches have influenced him.The hope of kingship produces the thought of the murder of the king.However the witches have never suggested this to him.Thus he falls victim to his own ambitions which have been fuelled by the witches.The predictio about Banquo was that he won't be the king himself but the begetter of the kings.It makes Macbeth feel insecure from Banquo's side.So he thinks of liquidating him along with his son.Again the pediction that none born of a woman would be able to harm him makes Macbeth feel secure.Another prediction about the Birnam woods makes him secure and he cannot read the ambiguity of their words.The slaughter of Macduff's family is the fallout of the predictions of the witches.
Both Macbeth and Banquo had met the witches.But they could not exert evil influence on Banquo.Evil is in mind.Macbeth becomes a prey to his soaring ambitions.The witches influence his decision to a great extent because Macbeth wants to make his ambitions a reality