Hello! You asked how supernatural forces interest themselves in the actions of Beowulf, and how they intervene from time to time.
In Beowulf, we find our hero battling a whole host of mythical dragons and demons; he has almost superhuman strength. When Unferth goads and challenges him, Beowulf wastes no time in regaling his listeners with the account of the time he slew nine sea-monsters. Unferth taunts Beowulf about his swimming match with Breca (he says that Breca won), but Beowulf simply admits that
We made agreement as the merest of striplings/ Promised each other...We simply kept an engagement made in early life... that we yet would adventure/ Out on the ocean
Beowulf says that he swam five nights on the ocean with Breca until the waves parted them. Beowulf states that he would not have otherwise parted from Breca:
He sure was unable/ To swim on the waters further than I could,/He could not excel me, and I would not excel him... nor would I from him go.
Here, we see the portrayal of Beowulf as a god-like king, who can swim in full battle gear for five nights and still possess enough residual strength to kill nine sea monsters. He has no need of boasting about his prowess when his brave deeds quite clearly speak for themselves. He tells Unferth that he will make Grendel, the demon-monster, fear the Geats. Like Hrothgar, we put our trust in this god-like king, who is courageous, competent and trustworthy. We are told that God himself has raised up a deliverer: through one man's "war might," this monster, this scourge on society, will be vanquished.
Beowulf defeats both Grendel and his mother with his God-given powers. Alas, when he tangles with the dragon, it is a Pyrrhic victory (a victory secured at such great cost that it is almost indistinguishable from straight defeat). Traditionally the dragon is a symbol of sin (the poet seems to mingle both pagan and Christian beliefs in Beowulf): the fight to the death illustrates the powerful Christian imagery of wrestling with evil. Even though victory may be secured, the path proves treacherously fatal. God grants Beowulf victory despite his age and despite the dragon's almost insurmountable power. Despite being doomed by the dragon's poison, divine Providence allows Beowulf to live long enough to pass on his kingly legacy of courage and honor to Wiglaf. Beowulf's Christ-like sacrifice has secured peace and treasure for his people, as well as a new king committed to the protection and happiness of those he rules.
Hope this helps. Thanks for the question.