Why was King Hrothgar in despair after the several murders if his kinsmen?

Hrothgar despaired because there was nothing to be done about Grendel's attacks. His castle was a place of death.... and by night it was ruled by a monster.

Grendel is opposed by God,loves tormenting the Danes,and seems to satisfy itself with the murderous acts at the Hall.if you were to note that the epic is really told at the period of Christianization who could Grendel represent? How does the author perceive Christianity in relation to the ills of the earth?