Lennox and other Scottish lords and soldiers discuss the situation: Malcolm and his army are at Birnam Wood. Macbeth, in a constant rage verging on madness, is fortifying the stronghold of Dunsinane.
With the mention of Birnam Wood and Dunsinane, the audience can see that Macbeth's fate is approaching.
The lords agree that Macbeth is tormented by his terrible actions, and that those who follow him do so out of fear, not love. The lords ride to join Malcolm.
Macbeth's efforts to maintain power through violence have, in fact, turned people against him and made him weak.