Beowulf is battling against evil because he sailed to the Danes to rescue them from Grendel. It is evident in lines 195 onwards to fight Grendel. SO when the night came, Beowulf and his warriors waited in the hall for Grendel to come. Together with his warriors, they sailed to help King Hrothgar defeat Grendel who continued to kill his men.
The author is giving details and purpose to this event and is inviting people to come to attend it. They even tell you how you can get to the event and about the designated "drop zones".
The lines represent how passionate a person’s emotion can be
when they are chasing for the ideal of justice, it reflects how Romanticism
defines another form of passion through the poem.