What is the purpose of the "Finnsburg Fragment"?

To the casual reader, Beowulf seems to center on the episodes involving Beowulf's killing of Grendel and, later, the dragon that plagues the Geat kingdom. As all scholars acknowledge, however, one of the poem's themes encompasses the struggles, often violent, among the Scandinavian tribes. For example, the most famous digression in Beowulf is known as the "Finnsburg Fragment" or the "Fight at Finnsburg" at lines 1067-1159, which re-tells a serious and destructive battle, based on betrayal, between the Danes, on one hand, and the East Frisians and Jutes, on the other hand. This lengthy digression is important because it allows the poet to keep tribal history and conflicts in the forefront of the minds of his audience, reminding them of their violent heritage and, perhaps more important, subtly contrasting the peaceful nature of the new religion, Christianity, with life in a pagan world. The Hermod and Sigemond digression serves a similar purpose.