MACBETH                  My name’s Macbeth.

YOUNG SIWARD        The devil himself could not pronounce a title

More hateful to mine ear.

MACBETH                              No, nor more fearful.

YOUNG SIWARD        Thou liest, abhorrèd tyrant. With my sword

I’ll prove the lie thou speak’st.

Fight, and Young Siward slain

MACBETH                              Thou wast born of woman;

But swords I smile at, weapons laugh to scorn,

Brandished by man that’s of a woman born.

Exit                  (5.7.8-14)

Macbeth tells Young Siward what, perhaps, he already knows, or has guessed: my name’s Macbeth. Yes, the one you’ve been hearing all the stories about: I’m the bogeyman who’s haunted your nightmares! Yaaaaaah! Young Siward continues to characterise Macbeth as a devil, or worse, and he stands his ground: the devil himself could not pronounce a title more hateful to mine ear; if Satan himself were to say, my name’s Satan, it wouldn’t be as bad. You’re the absolute worst; I hate you and everything you’ve done, everything you stand for. No, nor more fearful, Macbeth taunts him: you’re just chicken! I’m more frightening than the devil, and you’re more frightened of me than you would be the devil himself. Who are you calling chicken? Thou liest, abhorred tyrant, responds Young Siward, bravely, defiantly. I’m not afraid; are you calling me a liar? It’s that, the principal cause of a quarrel between gentlemen, the impugning of his honour, that Young Siward reacts to as much as, if not more than, the fact that he’s now face to face with Macbeth, the abhorred tyrant, the object of their hatred, the one they’ve come to kill. With my sword I’ll prove the lie thou speak’st. I’ll fight you to defend my honour and my good name, as much as to show that I’m not afraid, or in any other cause, even the killing of a tyrant, the liberation of a country, the restoration of a rightful king.

So, fight, and Young Siward slain. Probably not protracted—Young Siward is brave and honourable but inexperienced, and that’s pretty much the whole point of him—and Macbeth is going to fight dirty, brutal and efficient; no finer points of duelling or honourable single combat for him. Nice guys finish last, so far as Macbeth’s concerned. And besides, he’s been badly shaken by the appearance of Birnam Wood; this is the chance to recover some of his equilibrium, get his confidence back. Thou wast born of woman, he brags, over Young Siward’s bloody body. Ha! Swords I smile at, weapons laugh to scorn, brandished by man that’s of a woman born. I’m invincible again! I’m untouchable! Hubris, and famous last words, the couplet ringing hollow, surely.

Young Siward’s death is, in a sense, the last sacrifice of an innocent to Macbeth in the play—but it’s also a performance of valour and honour, courage and decency; his death isn’t entirely in vain. It’s part of the generational shift that Malcolm represents too. Another short scene done, and the fight continues.