"Upon her skinny lips: you should be women,
and yet your beards forbid me to interpret…"
This is because the actors performing the play at the time would have had no costumes and all the parts would have been played by men, so the audience would have had to imagine what the actual witches would have looked like. They greet Macbeth with three titles, "Thane of Glamis", "Thane of Cawdor" and "King hereafter". This we can tell shocks Macbeth as Banquo asks him why he looks so startled by the good news.
It is at this point that Banquo becomes interested in what the witches have to say and he is told that his children will become King. Macbeth continues with his questions, asking how he can take titles from people who are still alive. He says:
"…I know I am the Thane of Glamis; But how of Cawdor?"
The audience would know from the previous scene that the Thane of Cawdor has been sentenced to death, but Macbeth is unaware of this, yet they vanish without answering any of his questions.
We can tell that the confrontation with the witches has startled Macbeth, as he asks Banquo if he thinks that they are insane and imagined the whole thing. When Angus and Rosse arrive and tell Macbeth that the Thane of Cawdor has been sentenced to death for treason, Banquo's line:
"What! Can the devil speak true?"
shows the audience that he is shocked to hear the predictions come true and that he realises that they maybe are telling the truth, but he is not sure he can trust them because they are evil. It is at this moment that Macbeth starts to show signs of having split decisions, as he talks aside, showing his inner conflicts to the audience. He too, realises that two of the three predictions have come true and the only one remaining is to become King. Banquo, seeing his distant look, then warns him not to be taken in by the witches, as he believes that they are telling the truth in regards to minor details, but they cannot be trusted when it comes to important details.
At the end of Scene 3, the audience would feel shocked that the predictions had come true and would also be wondering how Macbeth could insure that the final prediction comes true as well.
In Act 1 Scene 5, Lady Macbeth is reading a letter written by Macbeth about his meeting with the witches. Upon finding out this information, she shows her evil side, asking the spirits to take away her feminine qualities so she can kill the King, Duncan, herself, as she knows Macbeth is too kind and she remarks:
"It is too full o' the milk of human kindness…"
This shows a relationship between her and the witches, and by the time Macbeth arrives, only a few minutes later, she has already geared herself up to killing Duncan. It is the witches' prophecies, together with Lady Macbeth comments towards his manhood that drives Macbeth to kill the King for his own gain.
We do not meet the witches again until Act 3 Scene 5, after the murders of the King and Banquo have been committed and all of the trouble regarding the disappearance of the Kings sons and the murder investigation begin. They again meet on the heath, together with the thunder to emphasise the confusion and disorder. They meet Hecate, the senior witch, who is angry with them for having dealings with Macbeth and she describes him as:
"…a wayward son…"
and one that is not devoted to witchcraft. She too predicts the future, as she tells them that Macbeth will come the next day and he will then learn his fate. The audience at this point would feel intrigued to what will happen to Macbeth and would be curious to know what the future holds for Macbeth.
We meet the witches again in Act 4 Scene 1 when Macbeth finds out his fate. Again, thunder sounds and the witches are found around a cauldron, chanting a spell. The ingredients they add to the mixture sound revolting, for example:
"Eye of newt" or "Witches mummy"
These ingredients would add to the witches' gruesome façade. When Macbeth arrives he refers to them as "black", "midnight" and "hags", showing the audience that he dislikes the witches. He asks them to use their evil powers to answers his questions.
When the apparitions appear they are coupled with thunder claps to represent the chaos and evil all around. The first apparition tells Macbeth to be wary of Macduff, which he comments is his biggest fear. The second vision tells him that any man born of women cannot hurt him. This, combined with the third apparition's prediction about Macbeth not being defeated until Birnam Wood moves to Dunsinane Hill, would add to Macbeth's feeling of power and invincibility. He asks if Banquo's children will still become Kings, and in answer, eight Kings appear, and they all look like Banquo. The audience can tell that this shocks Macbeth as he says:
"I'll see no more: - And yet the eighth appears…"
The witches then disappear. Lenox enters to tell Macbeth that Macduff has fled to England. Macbeth then shows the audience his inner thoughts by talking aside, when he decides that if Macduff is the only one who can hurt him, he must kill anything to do with him. This acting on impulse shows a change in Macbeth's character, as he doesn't ponder on all the aspects of the murder as seen when he was contemplating killing Duncan. This quick decision shows the audience that he has become more hardened towards murder and fears nothing. At this point the audience would feel worried for Macbeth's safety as they would already know, from the previous scene that Hecate that the witches had been deceiving Macbeth.
It is not until Act 5 Scene 6, when he finally realises that the witches have been lying to him, after a messenger report that the wood appears to be moving. The audience would know that this was Macduff's way of camouflaging his army, but Macbeth would be unaware of this tactic. He excepts that the witches have lied and that he has also been to confident and has overlooked what has actually been happening, and comments that if his is going to be killed, he might as well die fighting.
The second reference to him being deceived is when he says in Act 5 Scene 1 that:
"They have tied me to a stake…"
and then he carries on by saying:
"…I cannot fly…"
which shows that he has excepted that he cannot hide from his fate. The final reference to the witches lying, is when Macduff tells him, Act 5 Scene 8, that he was born by Caesarian. Macbeth has to except that the witches have lied to him. Macduff then kills Macbeth.
Throughout the play the witches, never actually suggest that Macbeth should kill anyone to ensure that the prediction came true. They merely used language to increase his confidence and his feeling of indestructibility and security.
The witches are in the play as they serve a variety of purposes. The most obvious role is to give Macbeth the initial ideas and to create the ambition within him. The witches also help to show the audience the changes that are occurring in the character as the play progresses, which can be seen through the way he talks to the witches. For example, he gets more and more familiar as he gets further away from the constraints of human society. On a more practical and theatrical level, the witches provide a change in scene and mood, which keeps the audiences' attention.
The message put across by the play about witches is that they are evil and not to be trusted. An audience in Shakespeare's time would have understood this message, as witches and witchcraft were very prominent and people were scared of the evil spirits. Nowadays the audiences see the witches as a dramatic device that adds tensions and drama to the plot of the play.
