Siward is a General of the British Army and Earl of Northumberland. Since he is Duncan's brother, he proclaims the British army against Macbeth. Soldiers of his army are masked by the branches from Birnam Wood, making the prophecy of the witches. The witches claimed that Macbeth would fall when Birnam Wood was removed to Dunsinane. He is very noble because he takes very courageously the loss of his son. It was very significant for him to find out how his son died. When he found out that he had died fighting at the front, he was finally able to put up with his loss.
Young Siward in the Essays