How may Beowulf's defeat of Grendel be described as the defeat of the "dark side" of the warriors's life?

In the epic poem, Beowulf, the hero
(Beowulf) defeats Grendel. Grendel represents darkness and evil. Grendel has been
banished into darkness given his ancestral link to Cain. Since his exile, Grendel has
been required to live only in darkness and cannot enter into the light. As the foe of
God, Grendel automatically becomes a foe of Beowulf.

The
epic is written from a Christian perspective. This means that the story supports
Christian theology and, therefore, the importance of good conquering
evil.

Beowulf, the Christian hero, must defeat God's foe,
Grendel. By conquering Grendel, Beowulf is able to show that God looks upon him with
favor. Therefore, his defeat of Grendel depicts the crushing of the dark side of life.
If Beowulf has a dark side, it is defeated by enacting revenge in the name of God upon
the hell-monster.