The Witches are supernatural in character and Satanic. They delivered a self-fulfilling prophecy to tempt Macbeth into willingly committing evil deeds to secure his soul.
A common motif in mythology is that of the three Fates. Greek and Roman, Irish and Norse legend all have versions of these figures with each of the women representing past, present and future respectively.
The Witches in Macbeth are often compared to the Fates, particularly their Norse incarnation, known as the Norns. They are described in the play as:
The weird sisters, hand in hand
And the word "weird" is derived from the old Norse "wyrd", meaning "fate". The Norns, unlike their classical counterparts, were outcasts who lived far from human habitation. It is clear from the events of the play that, like the Fates, are in the habit of predicting the future. But look at the way they greet Macbeth:
- All hail, Macbeth! hail to thee, thane of Glamis!
- All hail, Macbeth, hail to thee, thane of Cawdor!
- All hail, Macbeth, thou shalt be king hereafter!
He has been Thane of Glamis for some time. He is - although he does not know it - Thane of Cawdor. And he will be King in the fullness of time. Each statement is made by a different Witch, suggesting that, again like the Fates, they represent past, present and future.
Why does this matter? Because the purpose of the Fates was to control destiny. Indeed the Norns were so powerful that they held the destiny of not only men but gods, as well. So if we are to equate the Witches with the Fates, it strongly suggests that they knew full well what the result of their prophecy would be, and were fully able to ensure it would come about.
This begs the question of why they bothered to get involved at all. A possible answer is that Shakespeare's time is not so long after the days of witch trials. Audiences were still willing and able to believe in the supernatural, and in Satanic forces. And the Witche's modus operandi, which is essentially to tempt Macbeth into murder with their prophecy, echoes the classic behaviour of devils. Fates they may be, but by leading Macbeth willingly to his fate, they are ensuring his rejection by God and that his soul will go to hell.
Their Satanic allegiance is made clear at the very opening of the play. The first two witches call out
- I come, Graymalkin!
- Paddock calls.
"Graymalkin" (literally "grey cat") and "Paddock" are their familiars, helper devils in the form of animals. The belief in familiars dates back to the witch trials of earlier centuries and was central in many prosecutions.
Which brings us on to why they'd bother in the first place. To which the answer is that, as allies of the devil, they are simply and clearly agents of evil.
Look at the conversation they have among themselves prior to Macbeth's entrance, in which they are boasting of the wicked deeds they have done. The first witch has been killing pigs, offering no reason and thus leaving the audience to presume it was for the sheer hell of it. The second has bought down the most awful, ruinous curses upon a sailor for no better reason than his wife refused to share her chestnuts. If they are the Fates and servants of Satan, they need no further motivation.
- Frye, Roland Mushat. "Launching the Tragedy of Macbeth: Temptation, Deliberation, and Consent in Act I." The Huntington Library Quarterly.
There is no evidence that Shakespeare intended the three weird sisters to be witches!
As I have mentioned elsewhere there is legitimate scholarly opinion to the effect that Shakespeare did not include witches in his play. The modern notion of 'witches' is a misunderstanding: the text which modern academics ascribe to Shakespeare speaks of weird sisters not of witches.
There is much ambiguity in this play, as in many of his plays, due to corruption of the text during the process of printing it under the exceedingly primitive conditions so long ago. The printed text contains a good deal of textual corruption.
But, above all, it is now thought that some scenes which appear in modern editions of the play were added by another author, in the years between Shakespeare's death in 1616 and the First Folio printing in 1623. The references to witches are thought to have been added by another hand.
Calling them witches attributes supernatural powers to them, such as could account for their having an ability, with some credibility, to foretell the future. But although Shakespeare is still thought to have written the scene in which Lady Macbeth appears to urge her husband to murder King Duncan, some part of the ambiguity in her words can be accounted for by the fact that she may be referring to a rather different play than is currently included in modern printings.
For Shakespeare may have written her dialogue without witches in mind, and they may have been added by another author so as to strengthen Lady Macbeth's position in this scene, among others, where she needs to call on a supernatural prophecy that Macbeth 'wilt be King hereafter'.
The Folio text of 1623 is thought to be a revision of the original play, probably adapted by Thomas Middleton (and unquestionably using Middleton’s material, from his 1616 play The Witches). And Macbeth is very short by Shakespeare’s standards, suggesting abridgement.
He seems to have only had three 'weird sisters' in mind. Someone unknown, possibly Middleton, made the play a better box office attraction by inserting at least one extra scene with a reference to witches -- in the rest of the play the term was not originally used -- to give a better justification (in our eyes) for Lady Macbeth's claims that fate has prophesied that Macbeth will become king.
Her words, perhaps made ambiguous by simple textual corruption, but maybe because they originally referred to a quite different scene to the one now included in the play, have very little meaning. But the reason seems not to lie with Shakespeare but with the author who "collaborated" with him on the script - perhaps long after his death.
Indeed, Shakespeare's reference to 'weird' sisters in Act 1 scene 3 - originally spelled (i.e. before the modern versions) as in the old Norse fashion - and the fact that there are, tellingly, three of them, all seems to be more in keeping with their having been intended to represent the three Norse fates - beings with the gift of prophesy. A 16th century audience might have understood that reference rather better than we do -- who remembers the Norse fates today? Whereas 'witches' remains a concept which we do understand. So perhaps Middleton had a point.
Why did the witches give a prophesy? They didn't, they were added later, not by Shakespeare: he continues to speak of weird sisters, as in Act 1 scene 5, line 9.
Why did the weird sisters give a prophesy? Because they were intended to be the three Norse fates, who a 16th century audience would have understood to have the gift of prophesy.
In our terms, the three sisters represent the three spirits in Charles Dickens's A Christmas Carol: the ghosts of Christmas past, of Christmas present, and of Christmas yet-to-come.
Macbeth is a man, a real man, not a caricature. Like Hamlet, when he is urged by supernatural forces to commit murder, he recoils from the notion, and has to be talked into it -- in Macbeth's case by his politically ambitious wife. Macbeth is quite squeamish, she calls him a coward for being too full of the milk of human kindness (she actually uses that term: Shakespeare invented it, in this play). But her husband behaves like a real person might: he is sceptical of the so-called supernatural, and is unwilling to murder anyone, even King Duncan, just to fulfill his wife's political ambitions.
Shakespeare portrays the weird sisters as beyond human comprehension: we don't get any great insight into their motivation -- perhaps because this text is an abridged, greatly shortened version of the original. But most likely, much of what we do see of them is added later, and only their first appearance is genuinely by the author himself. Probably they are intended to be mysterious, beyond our comprehension. And the play is an exploration of Macbeth's comprehension of them, not ours.