Fourth sentence on the page. It's also discussed about a dozen times in other places on the page. It's not a huge plot point in the story, but it's definitely mentioned. Also, here:
Basically, Beowulf as we know it was put to paper by Anglo-Saxon monks, who wrote it in Old English and adapted it from Germano-Nordic. While doing so, they allowed their own biases to influence what they were writing, and occasionally made references to things that reflected their Christian world-view.
Most modern scholars accept that those elements almost certainly weren't part of the original story, but that's sort of the point.
Then the original story would have been completely different. It isn't a Christian work just because they stole it. ---