The great thing about a topic like this is that it has been written on extensively. An internet search will yield you a lot of ideas from other writers, which can help you build your essay. Here are some to get you started:
Beowulf is full of pagan ritual, yet the characters often exhibit spiritual strength arising from Christianity; character traits like meekness and poverty, and the decidedly Christian attitude of helping others, play a prominent role. This was a time when Christianity was new and the old pagan ways were sometimes fallen back on in times of stress. However, there is little doubt that the original epic poem pre-dates Christianity, so some changes were made over time to "Christianize" the tale. You might want to see if you can expand on this idea.
I hope this helps to get you going!