Malcolm and his troops have reached Dunsinane under the "leafy screens" of the branches, thus fulfilling the prophecy of the apparitions: Birnam wood has come to Dunsinane.
The strong sense of movement and of impending threat is generated throughout Act V by the swift alternation of scenes. This, the briefest of all the scenes, at a mere ten lines in length, enables the audience to follow the advancing forces of Malcolm and England virtually to the walls of Dunsinane castle.
Two lines are worth commenting on: First, Malcolm announces that Siward, his "worthy uncle" shall lead the first battle, while Macduff and he complete the encounter "According to our order." The phrasing of this, with the implication that Siward is to be revered for his age and experience, establishes very strongly the idea of propriety and orderliness in Malcolm's army, in contrast with the comparative lawlessness and lovelessness of Macbeth's regime.
The second point occurs in the stirring final couplet, in which the trumpets sounding the advance are referred to as "harbingers of blood and death"; a harbinger is a sign of what is to come, a precursor of Destiny or Fate.