Explicate the biblical allusion in reference to cain and abel and say what symbolic purpose it has here.

If you are talking about Beowulf, then Grendel is the representation of Cain. He is descendant of Cain, who committed the first murder ever. Cain and Abel were Adam and Eve's sons, and since Cain was jealous of Abel, he killed his own brother. Thus, every descendant of his is cursed, which is why Grendel is a monster.