In Act 5, Scene 2, the audience witnesses a conversation among a number of noblemen still in Scotland who are waiting for Malcolm's army to arrive from England. These men are Menteith, Caithness, Angus, and Lennox. They discuss the movements of the English army (brought by Malcolm) as well as the current activities of "the tyrant," Macbeth (5.2.13). They say that "Those he commands move only in command / Nothing in love." (5.2.22-23). In other words, even Macbeth's own army does not want to fight for him; they do it only because they have been ordered to.
In Act 5, Scene 4, Siward and Young Siward are added to this group, which now accompanies Malcolm and Macduff as they march toward Dunsinane, the location of Macbeth's fortress. The purpose of this scene is to show Malcolm's strategic way of concealing their army's numbers: each soldier is to "hew him down a bough" and hold it up in front of him (5.4.6). This is also the way one of the Weird Sisters statements to Macbeth comes to fruition: he cannot be harmed until Birnam Wood comes to Dunsinane Hill, and -- lo and behold -- it now appears that such a thing is happening!