The opening of Scene 3 does more than to simply recall us to the world of the supernatural of Act I, Scene 1: The Witches' curse of the sailor foreshadows what Fate has in store for Macbeth. The sailor is the captain of a ship, in the same way that Macbeth is to become "captain" of his land; like the sailor, Macbeth will be blown by the tempests of ill Fortune. Sleep will be denied to both. Famously, Macbeth later believes that, in murdering Duncan, he "has murder'd sleep," and both he and Lady Macbeth are denied "Sleep that knits up the ravelled sleeve of care." Finally, the metaphor of a storm at sea is traditionally used to refer to confusion and the unpredictability of events.
Macbeth's first words ("So foul and fair a day I have not seen") ironically recall the Witches' "foul is fair" in Scene 1, but Banquo is the first to spot the weird sisters, remarking on the Witches' ambiguous and confused appearance: They "look not like the inhabitants of the earth, / And yet are on it"; they seem to understand him, and yet he cannot be sure; they "should be women," and yet they are bearded. Later in the scene, Macbeth remarks that the Witches "seem'd corporal [physical]" and yet they vanish like bubbles "into the air."
No such ambiguity occurs in the response of the Witches to Macbeth: He is Thane of Glamis, he is Thane of Cawdor, and he shall be King. This contrast between what is uncertain and what is certain, or between what is confused and what is ordered or ordained by Fate, is one of the crucial structural components in the writing of this play, and it is clear that Shakespeare wants us to see it.
