Ryan Howse has provided a excellent brief summary of Beowulf and his contribution not only to Western culture but to fantasy fiction. The piece ends thusly:
Beowulf is one of the most influential texts in history, and it has a particular relevance for fantasy. John Gardner, the famous writer, wrote a take on the novel from the monster’s point of view, called Grendel. In this, Grendel was a figure of existentialism and angst who dies at the hands of the hero. Gardner also used Beowulf as a key text in his writing guide, The Art of Fiction: Notes on the Craft For Young Authors.
Michael Crichton wrote Eaters of the Dead, later turned into the film the 13th Warrior. Neil Gaiman and Roger Avary wrote a script forBeowulf that streamlined the narrative so that it followed causality, rather than the third tale being separate from the other two.
But of course, the most important reason that Beowulf is important is J.R.R. Tolkien. His love of Beowulf influenced Middle-Earth. Smaug is a literary descendant of Beowulf’s dragon, right down to the single piece of stolen treasure awakening him.
Do read it all. It’s short, and you’ll be better for it.