Young Siward is able to express the attitude toward Macbeth by those who would have formerly been his allies and supporters. Macbeth has gone from being
Brave Macbeth-well he deserves that name!
Young Siward is driven to execute Macbeth, who has so divided the nation that even his own troops fight among themselves and join Macduff's crusade.
The most notable function of young Siward, however, is to further convince Macbeth that he is invincible. Macbeth perceives no threat from young Siward, and rapidly dispatches him in combat. He is energized by his defeat of the brave young man-
Thou wast born of woman.
But swords I smile at, weapons laugh to scorn,
Brandish'd by man that's of a woman born.