In Shakespeare's Macbeth, the audience witnesses many different kinds of power.
As the play opens, we see the power of the Scottish army as it advances on its enemy. We see Macbeth's power as a great warrior for the Scots:
For brave Macbeth—well he deserves that name—
Disdaining fortune, with his brandish'd steel,
Which smoked with bloody execution,
Like valor's minion carved out his passage
Till he faced the slave… (I.i.18-22)
Macbeth, with fearsome blows of the sword, hacks his way through the crowd to face Macdonwald, the Scottish traitor. The Sergeant's report reflects his awe of Macbeth's ability not just to protect himself as he moved through the chaos of battle, but also to find his way to the villain who has betrayed king and country.
Another kind of power is illustrated in Lady Macbeth's ability to goad her husband into murdering Duncan. While Macbeth had already conceived a plan to clear his way to the throne, when he begins to have second thoughts Lady Macbeth exerts her power to make Macbeth question his male prowess by calling him a coward. While Macbeth becomes angry and defensive, it is not until Lady Macbeth declares that she could murder her own newborn child if she promised to do so that we see Macbeth's intentions return to contemplation of murdering his king and friend. He seems to see his wife through new eyes as she wields her power over her husband, as she outlines the bloodthirsty way they will take Duncan's life (and his guards' lives)—when he is asleep with too much wine and unable to defend himself:
When in swinish sleep
Their drenched natures lie as in a death,
What cannot you and I perform upon
The unguarded Duncan? (I.vii.75-78)
We see Macbeth's power grow as he arranges the murders of Banquo and Macduff's family. Banquo had to be killed because he heard the witches' predictions in Act One about Macbeth becoming king, and he grew suspicious when Duncan was murdered in Macbeth's home. Banquo has the power of truth in hand that threatens Macbeth's place on the Scottish throne—something Macbeth cannot withstand.
Later, when Macbeth learns that Macduff has fled to England, Macbeth orders the murder of Macduff's family:
The castle of Macduff I will surprise,
Seize upon Fife, give to th' edge o' th' sword
His wife, his babes, and all unfortunate souls
That trace him in his line. (IV.i.166-169)
While the witches do not seem very powerful at the beginning, Macbeth becomes so dependent upon them by the end of the play that he disregards caution and common sense, believing that no one can harm him. Their power is shown in their ability to predict the future and to tell him half-truths, which he believes. When bigger lies follow, Macbeth has already grown to depend on the veracity of everything the evil witches tell him. The witches have predicted that a man born of a woman cannot harm him.
After Macbeth kills Young Siward in battle, Macbeth declares:
Thou wast born of woman.
But swords I smile at, weapons laugh to scorn,
Brandish'd by man that's of a woman born. (V.vii.15-17)
Macbeth literally believes that no man in the world can harm him. However, though Macbeth faces Macduff with confidence, the tyrant soon learns that the witches have lied to him. Confronted by Macduff, Macbeth warns:
I bear a charmed life, which must not yield
To one of woman born. (V.viii.15-16)
However, Macduff explains why Macbeth does not live a "charmed life."
Despair thy charm,
And let the angel whom thou still hast served
Tell thee, Macduff was from his mother's womb
Untimely ripp'd. (17-20)
Macduff was born by a caesarian section rather than a traditional birth. He is able to kill Macbeth. In this we see the power of the witches to play word games and to convince a man to give his soul over to evil (which is what Macbeth does when he kills Duncan because it is a mortal sin to kill a king). We also see the righteous anger and power of Macduff as he wreaks vengeance upon Macbeth for the death of his family upon Macbeth's orders.
Macbeth's story includes many different kinds of power: the power exerted by physical force; the power of words; the power of the supernatural; and, the power of justice and of truth.