In Act V, scene 7, what is the dramatic importance of the fight between Macbeth and Young Siward?
The scene serves several purposes. First, killing young Siward assures Macbeth that he is invincible; the young man was indeed "born of woman" and therefore he could not harm Macbeth. The king feels hopeful that he will be successful in rebuffing the attack on Dunsinane. He wins this battle, of course, because he is a skilled, experienced soldier while young Siward has hardly any experience whatsoever. Despite his lack of skill, however, the young man does not shy away from the fight; he battles valiantly. Because he dies with his "hurts on the front" (he was wounded on the front, not the back, which would mean he was cowardly running away), his father Siward is proud of him.
In the final act of the play, which is a series of short scenes moving back and forth from outside the castle to the interior of the castle, this scene helps to move the plot forward even more quickly because Macbeth will fight with more conviction, believing that he cannot be defeated. His hopes are false; he is not immortal after all.
This scene also helps to reinforce the idea that the greatest effects of political tyranny are not merely national in scope but are also very personal. Families are destroyed by the tyrant Macbeth throughout the play. In the beginning, Macbeth kills King Duncan, his cousin, and forces the King's two sons to flee the country for safety. Then Macbeth hires two murderers to kill Banquo and his son. Fleance escapes, but is not heard of again in the play. Later Macbeth orders the killing of Lady Macduff and her son. Young Siward, the son of the English General, is also killed by Macbeth at the end. Macbeth is also to a great extent responsible for the death of his wife. An heir to the throne was of utmost importance to the king, and so the idea of national security is tied with security of sonship. It is ironic that Macbeth is childless during the action of the play.