Many elements in the epic show an amalgamation of paganism and Christianity. Let me name a few of them for you.
Right from the beginning we read of Grendel's mother. She is: "From [Cain] sprang many a devil sent by fate"(43). From this quotation we can see a welding together of Christianity and paganism. On the one hand, the idea of fate is not a Christian idea, but one that resonates with paganism, which goes back to the Greeks and Romans. On the other hand, Cain is from the book of Genesis. Cain is the one who killed his brother. Therefore, according to the Bible, Cain represents an unrighteous line of people.
From a broader perspective, all the fighting and the glories of fighting are pagan. What makes it also Christian is that the fighting is the fighting of evil. This quote will show the former:
[A] hilted weapon, a rare and ancient sword named Hrunting. The iron blade with its ill-boding patterns has been tempered in blood. It had never failed the hand of anyone who hefted it in battle, anyone who had fought and faced the worst in the gap of danger. This was not the first time it had been called to perform heroic feats (ll 1457-1469).
These words could have been written in any pagan culture.