The line you've chosen from Beowulf is a great example of the caesura, an important structural element in both Beowulf and Old English poetry as a whole. The caesura is a midline pause used throughout Beowulf, and it provides the poetry with an integral rhythm and structure that improves the flow of the verse. In this particular line, the caesura is important because the rhythm it creates heightens the sense of suspense. In the section of the poem that this line occurs in, Grendel is coming out of the wilderness with violent, murderous intent. The caesura here is vital because it creates a suspenseful atmosphere that perfectly mirrors the oncoming monster. Thus, we see that the caesura is important not only because it promotes rhythm throughout the poetic verse, but also because it makes the overall attempt to tell the story more effective.