Beowulf is one of the oldest documented epic poems in the Old English language. The written manuscript was produced between 975 and 1025, but we do not know when the actual poem was first spoken. We also do not know who the original poet was. We refer to that person(s) as the “Beowulf poet.”
In the poem, Beowulf, a great hero, comes to the aid of the tormented Danes. He slays the monster Grendel and then Grendel's monster mother, and eventually kills a dragon. He dies battling the dragon, but manages to rid the land of its monsters.
It is important to consider what context the poem was created in--because the language praises traits that are different from what contemporary literature mentions. In passages such as the one in question here, we see a significant amount of blood and action, and a minimal amount of emotion. That is because in the time period of the tenth century, the people who lived were the people who fought. Being valiant and brave was necessary in order to become successful. Death was a common occurrence, and the ability of a man such as Beowulf to fight against it was, in essence, a fight against fate itself. Thus, the sections of the epic poem that seem over-the-top and overly heroic (think superhuman strength and impossible swimming abilities) are evidence that Beowulf is a true hero. If Beowulf had regular human capabilities, or if his great strengths were not praised, the poem would not be as fantastical or exciting.
The descriptions of Beowulf's warrior prowess function to remind the reader's of his heroic capabilities, primarily his strength and bravery. Because those traits were necessary of successful men in the tenth century, they were significant and exaggerated within the epic poem Beowulf.