One way you can explore the dynamics between good and evil is by looking up how Christianity and Christian theology play out in Beowulf. The poem is a combination of Christianity and Germanic warrior values, so there are many Christian themes. For instance, the very fact that Grendel is said to come from the line of Cain is significant. Cain is the first murderer of the Bible. He killed his brother Abel, because he was jealous of him. Cain, therefore, represents an evil line. You might also want to explore Beowulf as a Christ figure. Trace the theme of sacrifice. Finally, another point of contact is the home of Grendel and the biblical depiction of hell (Revelation 21:8). These comparisons should get you off to a good start.
Good versus evil is a common theme in Beowulf. Beowulf represents good and the three monsters represent evil. Beowulf is the larger than life hero who kills/conquers the evil Grendel, Grendel’s mother and the dragon.
Beowulf is a mighty warrior from the land of the Geats. He has heard of the terrible monster, Grendel, and leaves his homeland to help Hrothgar, the lord of the Danes. He is courageous, bold and stronger than any of Hrothgar’s warriors.
Grendel is established as being evil because he is a descendant of Cain, the first murderer. He terrorizes Herot for twelve years. He attacks the Danes because of their merriment and joy. The Danes mention God in their songs and this infuriates Grendel.