Answer:
Because of the shaper.
Explanation:
Grendel fears Hrothgar because of the Shaper. The Shaper has made Hrothgar so much more of a magnificent figure than he was before. In sense, the Shaper "shaped" Hrothgar's feats and reputation to a more amplified one, making Grendel fear the new and great Hrothgar by the skill of poetry and speech.
