Why is it important that Shakespeare presents Macbeth as a warrior in act 1, scene 2, and how does he do it?

In
act 1, scene 2, of Shakespeare's , Kingcalls on a Sergeant to tell the
story of the battle in which he was just wounded. This is the Sergeant's, and Shakespeare's,
opportunity to praisefor his decisiveness, skill as a warrior, and unwavering courage in battle,
even in the face of overwhelming forces aligned against him.

Just as Macbeth
kills Macdonwald in one-on-one combat and sends Macdonwald's army into full retreat, the King of
Norway arrives with fresh reinforcements and renews the attack on Macbeth's army. Macbeth
defeats the King of Norway's army and wins the day for King Duncan.

Following
his victory in two battles against Duncan's foes, Macbeth is at the height of his glory. Duncan
commends him for his bravery and rewards him with the property and title of the traitorous Thane
of Cawdor.

Interestingly, Shakespeare foreshadows Macbeth's later behavior
toward Duncan by assigning him the traitorous Thane of Cawdor's title.

Nevertheless, by raising Macbeth so high, Shakespeare can contrast the height of
Macbeth's hard-won glory with the ignominy of his precipitous fall from such a great
height.

Whereas the loyal warrior Macbeth is decisive and fearless, the
ambitious, traitorous Macbeth is cautious, indecisive, and fearful. Shakespeare shows the
deterioration of Macbeth's once-noble mind into madness, melancholy, and despair, which
culminates in Macbeth's last futile act of courage againstand Macbeth's ultimate
demise.