This short scene develops the drama of the preparation for battle. In language that recalls that of Act III, Scene 6 and Act IV, Scene 3, the characters remind the audience of the various military alliances between Malcolm, England, and the rebel Scots. In this sense, the scene is simply a plot-filler, but there are three points to note: First, the audience is introduced once more to the fateful name of Birnam Wood, which the Third Apparition in Act IV, Scene 1 prophesied to be the downfall of Macbeth.
Second, Caithness' portrait of Macbeth comes close to the description of a warrior-hero given by the Captain in Act I, Scene 2, especially in the phrase "valiant fury," but now the anger is not righteous: It arises from a "distemper'd cause" which Macbeth can no longer "buckle . . . within the belt of rule." Again, in another metaphor of clothing, Caithness adds that Macbeth's royal title "Hangs loose about him, like a giant's robe upon a dwarfish thief." (It is likely that nearly three centuries later, Robert Louis Stevenson was thinking of this line when he described the malicious dwarf Edward Hyde wearing the outsize clothes of the respectable Mr. Jekyll.) In Act I, Scene 3, Banquo talked of Macbeth's honors as "strange garments" which "cleave" (conform) to the shape of the body only by constant use. The metaphor is exact: Macbeth's title no longer fits him.
Third, the tone of the rebel Scots is one of uncompromising courage. Once more Scotland is described as a sick patient, the only cure for which is "each drop" of their own blood spilled in their country's defense.
