Why does Beowulf not kill himwhy does the frisian not try to attack beowulfwhy does Beowulf feel invicible?

Beowulf does not kill Grendel's mother because she is also a mother seeking revenge for her son. The Frisian king does not attack Beowulf out of fear and respect for his strength and bravery. Beowulf feels invincible due to his past victories in battles, his belief in fate, and the support of his loyal comrades.