Grendel's Motivation In Beowulf

Grendel is a man-eating demon that lives in the land of the Spear-Danes and attacks King Hrothgar's mead-hall, Heorot, every evening. The narrator of Beowulf claims that Grendel's motivation is hearing Hrothgar's bard sing songs about God's creation of the world, which rubs his demonic nature the wrong way. Whatever the reason, every night Grendel slaughters more Danes and feeds on their corpses after tearing them limb from limb. Although he can't be harmed by the blade of any edged weapon, Grendel finally meets his match when the Geatish warrior Beowulf takes him on in a wrestling match.
Cannibalism, curses, and Cain, oh my!

The poet explains that Grendel and his mother are the descendants of the Biblical Cain, which suggests not only