King Hrothgar becomes sad because he foresees the trappings of Beowulf's hubris. Beowulf chose to fight Grendel barehanded to showcase his great strength and bravery. King Hrothgar knows that a truly good king would never take such an unnecessary risk simply for pride. See the link entitled King Hrothgar in Beowulf-King Hrothgars speech to Beowulf in Hall of Heorot in the related links section for an analysis of Hrothgar's warning about hubris.
After the initial joy of Grendel's defeat, Grendel's mother seeks revenge by attacking Hrothgar's kingdom. She kills one of Hrothgar's closest advisors, creating further sorrow and fear among the people. This leads to Beowulf's decision to journey to the underworld to face Grendel's mother and bring peace to the kingdom once more.
Hrothgar leaves Beowulf in charge of Heorot because Beowulf successfully defeated Grendel and his mother, ensuring the safety of the hall. Hrothgar trusts Beowulf's leadership capabilities and valor in defending the Danes from further threats.
Grendel's mother comes to avenge her son.
Beowulf responds to Hrothgar's appeal for further help by acknowledging the continued threat posed by Grendel's mother and offering to track her down and defeat her. He expresses his willingness to face any danger to protect the kingdom and ensure its safety.
A very good question! Many are killed in the early days of Grendel's attacks, but presumably Hrothgar simply stopped using the hall for feasts and kept his men away. He certainly has followers ready to do his bidding; he maintains his coast guard who welcomes Beowulf to Denmark and also a door-warden who challenges the party as to their business. Later we hear of a troop of young men who go riding out along the trail and Grendel's mother kills Aeschere, an older earl of the company. It is a good question because there is the issue of what is denied to Hrothgar by Grendel: his hall and crucially his gift-stool. The best warriors were drawn to liberal lords eager to share wealth. If Hrothgar could not attract such men, his following may have been less than impressive. The character of Unferth for example seems to have esteem in Hrothgar's hall, yet it would appear that he was a fratricide; not a man that most lords would entertain. Perhaps Hrothgar was not in a position to be choosy.
In "Grendel," details such as his immense physical strength, his ferocity in battle, and his supernatural abilities contribute to understanding the threat he poses. Additionally, his relentless attacks on the Danes and his reputation as a monstrous being who cannot be defeated by conventional means further emphasize the danger he represents.
In the epic poem "Beowulf," Grendel is described as a descendant of Cain, who committed the Biblical sin of fratricide. Grendel's violent attacks on King Hrothgar's hall and his merciless killing of warriors are seen as embodying chaos, darkness, and a malevolent force that threatens society. Additionally, Grendel's physical appearance - described as monstrous and inhuman - further emphasizes his symbolic role as an embodiment of evil.
Hrothgar's speech praises Beowulf's bravery, strength, and heroism in battling Grendel, highlighting his exceptional courage and prowess in combat. He acknowledges Beowulf's noble lineage and his willingness to face challenges head-on, which are characteristics typically associated with epic heroes in literature. Hrothgar also emphasizes Beowulf's selflessness and willingness to help others, qualities that further align him with the traditional epic hero archetype.
Grendel most likely returns Unferth to the king's mead hall as a way to taunt and intimidate the humans, demonstrating his power and control over them. It serves as a warning to the king and his people to not provoke Grendel further.
As a result of having captures and killed monsters on both land and sea, Beowulf meets the criteria for fighting Grendel. Known to be a brave warrior who is stronger and better suited for gallantry than most, Beowulf savors the challenge and is quick to volunteer his services to Hrothgar to fight the beast.
While Grendel's mother is hard for Beowulf to defeat, he IS able to use a sword, where as he has to battle Grendel bare handed.
Beowulf hangs Grendel's arm from the rafter as a trophy and proof of his victory over the monster. It also serves as a symbol of his bravery and strength to the people in Heorot. It is a way for Beowulf to showcase his success in defeating Grendel to further solidify his reputation as a legendary hero.