A terrible monster haunts the halls of Herot. Beowulf has to fight this evil fiend. No doubt, the reader sympathizes with Beowulf for he will have to fight this monster. After hearing the details of Grendel's awful attacks, anyone would be afraid to encounter Grendel:
[Grendel] arrived when the soldiers were sleeping and attacked, killing 30 of them. There were tears and laments, but he attacked the next night as well. The soldiers realized they must stay away from Herot in order to be safe and did so for 12 years, much to Hrothgar’s grief.
In Beowulf, the reader is encouraged to sympathize with Beowulf. Beowulf has to fight a horrendous monster. His life is endangered. Beowulf has to attempt what no other warrior has been able to do--to kill Grendel:
Grendel haunts the hall by night for twelve years. The Danes despair of ridding themselves of him. They can neither defeat him nor come to terms with him.
Grendel has been spreading havoc on the people for years. Beowulf is expected to face serious consequences by fighting Grendel. Grendel is a terrible monster whom no one has been able to defeat.
The reader sympathizes with Beowulf due to the severity of his task. Grendel is a monster who is killing the people. Grendel has been terrorizing the people for twelve years. This has gone on long enough.
Although Beowulf has put his own life in danger, he is not supported by all the court officials. The reader again sympathizes with Beowulf because a certain court official tries to discredit Beowulf:
Unferth, an official of the court, attempts to discredit Beowulf with the story of a swimming match Beowulf had as a boy with another boy, Breca.
It isn't enough that Beowulf is willing to risk his life to fight Grendel and save the Danes, but he also has to defend himself against the court official's attempt to discredit Beowulf.
Of course, Beowulf shares his side of the story and convinces the King to allow him to fight Grendel:
Beowulf exonerates himself with his version of the swimming match.
Ultimately, Beowulf fights Grendel and defeats him. Beowulf also defeats Grendel's mother. Although the reader initially sympathizes with Beowulf, Beowulf is triumphant and the reader is delighted to share in his victorious defeat of the monsters.
Lastly, the reader sympathizes with Beowulf at the end of Beowulf's life. Beowulf has led a solitary life with no family with whom to share his possessions:
There is no wife, no child, no kinsman, no friend to do so. Beowulf led a successful life as far as his victories and the 50 years of his rule, but he led a solitary life, apparently not by choice since he mentions ruefully several times that he has neither son nor heir to whom he can leave his possessions.
In the end, Beowulf dies. He is defeated by a dragon. The reader is saddened and sympathizes with Beowulf at his death. The people of his kingdom are equally saddened by his death:
While Beowulf died as he chose, Wiglaf questions if this was a wise decision. His people are weeping, leaderless, and in danger of imminent attack as soon as their enemies hear of their leader’s death.