Respuesta :
well beowulf was an epic peom so there is no first hand source to tell you why. It was a story that was passed down from generation to generation.
Explanation:
I think this made for a more understandable plot point for people, as most of them were, who had never read the play before. Hrothgar would have had made a deal with the Devil and Grendel would have been the consequence. It's the sort of bargain that we might see in Faust or Macbeth.