Allusion in Beowulf
The poet alludes to the biblical story of Cain and Abel, in which after Cain killed his brother, God cast him out of human society. All of Cain’s descendants also became outcasts and eventually monsters. Grendel is established as a kinsman of Cain, supporting the idea that he was human at one time.
The digression here to the story of Sigemund serves several purposes. First, by linking Beowulf to the cultural hero Sigemond, Beowulf is praised and his reputation is greatly enhanced. Second, the inclusion of this tale is meant to foreshadow more conflict in Beowulf's life.
The poet links Beowulf with the the legendary hero Sigemund, from a series of tales from the Old Norse Volsunga Saga that an Anglo-Saxon audience would know. The effect is to build on an existing narrative and perhaps foreshadow coming events in Beowulf's own story.
In a typically Scandinavian / Anglo-Saxon style, Hrothgar's storyteller performs another story for the audience, known in the poem as "the Finnsburg Fragment" or "Fight at Finnsburg." The story he shares doesn't include much detail beyond summarizing main events, which is likely an indication that the audience would be familiar with it.
To better describe the gifts bestowed upon Beowulf to his audience, the poet alludes to the tale of Hama, a heroic character in Germanic legend. Hama entered the castle of King Eormenric, a very oppressive Goth leader, and stole a priceless gold necklace, once thought to have belonged to the Norse goddess Freyja. In order to escape Eormenric's vengeance, Hama spent the rest of his life in the safety of a monastery.
The poet alludes to the Biblical story of the flood and Noah's Ark, in which God flooded the Earth to purge it of sin and evil. While this story would not have been known to Beowulf or Hrothgar, the poet reminds his audience of the power of God and the punishment of heathen creatures.