How do the attitudes of Macbeth's soldiers differ from Malcolm's? It is in Act 5 of Macbeth.
Malcolm's men fight for him because they respect him as the rightful king of Scotland; on the other hand, Macbeth's loyal followers dwindle as many have come to see him as a usurper. In Act V, scene 2 in the conversation between Menteith, Caithness, and Angus, the audience learns firsthand how Macbeth's men have changed their attitude. Caithness remarks that Macbeth's soldiers have lost the heart to follow a leader they do not trust:
Now minutely revolts upbraid his faith-breach;
Those he commands move only in command,
Nothing in love. (V.ii.21-23)
Macbeth's men lack the motivation to fight; many have already turned against him to join Malcolm's forces. In Malcolm, the men have found their true king; for him, they are willing to lay down their lives, whereas Macbeth's claim to the kingship fits poorly like a "giant's robe upon a dwarvish thief" (V.ii.25). Macbeth's evil deeds have at last caught up with him, and even his would-be supporters now find him small in stature compared to the greatness of Malcolm.