Beowulf is the greatest of the surving works composed in Old English. An Epic poem, Beowulf was composed orally in a form of poetry in which each line is effectively split in half, with the first half linking with the second alliteratively. It is the epic story of Beowulf, the man's man, a badass whose dark side you would not want to experience. He embodies all of the social ideals of the culture that created him: loyalty, honesty, courage, justice, and generosity. Despite much of the blood and horror, Beowulf proves to be a story of good versus evil and one man's quest to become immortal through fame. (The Geats did not believe in much of an afterlife, therefore the only way to live beyond death was by the legends you inspired.)
Believed to be composed circa 700 c.e., Beowulf has instances of blatantly obstrusive Christian influence in an otherwise pagan work. The snippits of Christianity were likely inserted by a priest who recorded the narrative in writing. (Priests were practically the only people in that day who were literate, and they probably didn't like all of that profane, godless paganism.) Apparently the priests would insert bits of Christianity (who knows what they took out?) as not to fully corrupt anyone who might read Beowulf. Take, for example, this passage:

At times they prepared sacrifices in temples,
war-idol offerings, said old words aloud,
that the great soul-slayer might bring some comfort
in their country's disaster. Such was their custom,
the hope of the heathen; they remembered Hell
in their deepest thoughts. They knew not the Lord,
the Judge of our deeds, were ignorant of God,
know not how to worship our Protector above,
the King of Glory. Woe unto him
who in violent affliction has to thrust his soul
in the fire's embrace, expects no help,
no change in his fate! Well is it with him
who after his death-day is allowed to seek
the Father's welcome, ask His protection!

So Healfdene's son brooded continually
over his sorrows; the wise man could not
ward off the trouble The strife was too great,
hateful, long-lasting, that had come to the nation,
cruel spirit's envy, gigantic night-evil.

Notice the completely obvious intrusion in italics.
Beowulf is idealistic and grand in nature. Many times there are great exaggerations (consider the time he falls through the water for "hours") and extensions of truth. Themes that are prevalent in Beowulf are Good versus Evil, famehogging, and the idea of ubi sunt. In every age those living look back to the great deeds of those deceased, and more often than not, they mourn. Because those days are over, and it is all generally going to shit.