Anglo-Saxon culture that it was important to risk your life to win battles, especially battles for revenge of loved ones. The big mother presents this aspect of Anglo-Saxon culture because she risks to fight and avenge her son's death.
Explanation:
The Anglo-Saxon heroic code put the battles on a level of high importance, for them the battles were more important than life itself. This intensified when the battle was aimed at avenging a relative or a friend. For the Anglo-Saxons a true warrior would risk his own life if it meant getting revenge for vile acts that someone committed with his loved ones.
Grendel's mother is a strong example of this concept, as she sets out to fight the powerful warrior who killed her son to avenge him. She knows that the warrior can kill her too, but she prefers to risk her own life so that her son can be avenged.
