In many ways, Beowulf is the simplest kind of epic there is. It's about the conflict between a courageous, mighty, loyal warrior and the demons and dragons of hell itself. The forces of good battle the forces of evil again and again, knowing that one day they will be defeated, but at least they'll die fighting. Of course, "good" in Beowulf means "strong, generous, and proud," and "evil" means "demonic creatures from the marshes." This particular battle between good and evil isn't as much about morals as it is about fate – and reputation.
Beowulf's most important conflicts are with demons and monsters, emphasizing that he is a heroic defender of humanity, rather than just one more strong-armed medieval warrior.
Beowulf can only take heroic action against fantastic creatures like demons and monsters, which suggests that real heroism is impossible in the context of mankind's wars between different tribes and factions.