Why might the poet have chosen to describe Hrothgar and Grendel in terms of their relationship to God?

Hrothgar is forever worshipping God or deities while Grendel essentially hates God. Lets face it; Grendel's life isn't so great. The endless songs of worship he hears coming from the Great Hall infuriates him to know end. Being a descendant of Cain doesn't help Grendel with his sense of identity either.