The bloody sergeant came before King Duncan to report on the battle at hand. He commended Macbeth and Banquo. When he compared their anxiety or fear of the battle, he compared Macbeth and Banquo to sparrows who are afraid of the great eagle. Also, the sergeant added a comparison of Macbeth and Banquo to a hare (a rabbit) that is afraid of the lion. Macbeth and Banquo were afraid of the army. Still, this did not stop Macbeth and Banquo. In fact the sergeant goes on to say that Macbeth and Banquo just made double their strokes with their swords. In other words, they fought doubly hard and became the heroes at the end of battle.
As sparrows are by eagles, or the hare is by the lion.
If I say truth, I must report they [Macbeth and Banquo] were as upset [afraid]
As cannons overcharged with double cracks.
So they doubly re-doubled strokes upon the enemy.
Whether they meant to bathe in fresh, bleeding wounds,
Or create another Crucifixion scene,
I cannot tell.
The sergeant used a great comparison to show the fear that Macbeth and Banquo had. He showed that Macbeth and Banquo were like sparrows fighting against a great eagle. Also, the sergeant showed a comparison of Macbeth and Banquo as a hare or rabbit fighting against a great lion. There is really no comparison. Macbeth and Banquo used sheer determination to come against a great army of soldiers. Through great effort, Macbeth and Banquo fought and won the battle. The sergeant was just reporting on their gallantry or bravery.