Final answer:
Unferth tries to frighten Beowulf by questioning his past deeds, specifically referring to a swimming match against Breca where Beowulf allegedly lost and faced grave danger.
Step-by-step explanation:
Unferth, seeking to undermine Beowulf's reputation, brings up the story of Beowulf's supposed defeat in a swimming match against Breca. By referencing this event, he aims to instill doubt or fear in Beowulf's mind regarding his capabilities or past achievements.
Unferth implies that if Beowulf couldn't succeed in the past, he might not be able to overcome the challenges presented by Grendel. This tactic attempts to weaken Beowulf's confidence and cast doubt on his ability to face the impending threat of Grendel.
This tactic of Unferth is strategic, aimed at shaking Beowulf's self-assurance by indirectly calling into question his past feats. Unferth's goal is to create uncertainty in Beowulf's mind regarding his own capabilities, hoping to weaken Beowulf's resolve and confidence before the impending battle with Grendel.