Answer:
The inclusion of the swimming competition is important because it shows a defeat for Beowulf and humanizes him, in addition, this defeat makes some people doubt the ability of Beowulf to win Grendel in a battle.
Step-by-step explanation:
Beowulf and Brecca have a silly swimming competition to test which one is a better swimmer. During the competition, Beowulf is attacked by sea monsters and ends up losing to Brecca, who becomes the best swimmer in the region.
This defeat makes many doubt whether Beowulf is really capable of defeating Grendel. Because the battle against Grendel will not be silly and easy and Beowulf was unable to defeat a simple man in a silly swimming competition.
This teaches us that Beowulf, despite all his strength and heroism, is a human being, like so many others, susceptible to failure and defeat.