Why is Grendel uneasy at the end of chapter 9?

Although Grendel had intended to slaughter the priests, the last priest’s talk of religion squelches his bloodlust. Grendel himself has reached a point where he is rebelling simply to rebel, turning his original attempts at existential self-assertion into a form of hypocrisy. He no longer believes his war against Hrothgar has any meaning, but he continues it nonetheless.