What pagan belief leads Beowulf to decide to go to help Hrothgar? :\?

Answer 1

In the legends, no specific "pagan" beliefs are mentioned... Beowulf helps Hrothgar because Hrothgar is plagued by a problem (Grendel) that could threaten many more people, and because he has family ties to Hrothgar. Helping someone in that case isn't a matter of religious beliefs.

However, if you're looking for the spiritual beliefs that may have influenced his decision, and how he decided to help, you may want to look into the Nine Noble Virtues, are a list of moral traits that were distilled by modern Asatru people from ancient Nordic literature, mainly the Hávamál.
The most common version of the list is:

Courage
Truth
Honor
Fidelity
Discipline
Hospitality
Industriousness
Self-reliance
Perseverance

There's an essay about them at http://www.friggasweb.org/nvirtues.html

Answer 2

I'm not sure about a Pagan beleif. As I remember it, Beowulf did it for fame and fortune. It's been a long time and I've never done an in depth study though try this link. Maybe it has what you need:

http://www.missmacsenglishclass.com/Bwulf1.htm

Answer 3

i was to up hold the weak and for the love of battle