The bloody sergeant compares the battle to storms, and Macbeth and Macdonwald as swimmers.
Duncan requests that the sergeant report on the battle between Macbeth and Macdonwald. He praises Macbeth’s courage and resilience, comparing the two to “two spent swimmers.” Yet Macbeth triumphed over him.
As whence the sun ’gins his reflection
Shipwrecking storms and direful thunders break,
So from that spring whence comfort seem'd to come
Discomfort swells. (Act 1, Scene 2)
The sergeant points out that even as the tide turned, it did not discourage Macbeth. He kept fighting, and defeated not only Macdonwald but his army, winning the battle for Scotland.
Duncan is so impressed with Macbeth’s courage and loyalty in this vividly described battle that he awards Macbeth with a promotion to Thane of Cawdor. Since it is the first of the prophecies to come true, it is one of the things that spurs Macbeth to kill Duncan.
Storm imagery is prevalent in this play. The witches use it, and it is often referred to by different characters. It symbolizes the lack of control people in the play have, as they are at the mercy of larger forces that they cannot control.