they are protected by magic
If you have read the book "Grendel", then you will know that the fire dragon, whom Beowulf fights later, charmed Grendel. That charm made him invincible against weapons, however he was still vulnerable to brute strength.
The weapons of Beowulf's warriors are ineffective against Grendel because Grendel put a spell on there swords to not pierce his skin.
none. he has a spell placed on him so that no weapon my hurt him.
The weapons of Beowulf's warriors are ineffective against Grendel because Grendel put a spell on there swords to not pierce his skin.
In the epic poem "Beowulf," Grendel and his mother possess special powers that render them immune to conventional weapons. Grendel's skin is impervious to swords and other conventional weapons, making it difficult to harm him. Similarly, Grendel's mother is protected by enchantments and possesses superhuman strength, which also makes her resistant to traditional weapons.
tears of Grendel's claw and shoulder without any weapons.
save Hrothgar and the Danes from the monster
No one else was able to defeat Grendel because he was protected by a magical charm that made him impervious to weapons from humans. Beowulf was able to defeat Grendel because he fought him with his bare hands, which allowed him to overcome the monster's defenses.
Grendel fights without weapons, so Beowulf chooses to do the same.
The weapons of Beowulf's warriors are ineffective against Grendel because Grendel put a spell on there swords to not pierce his skin. His ancestor Cain bewitched all weapons so they could not harm him.
Grendel avoids touching Hrothgar's throne as it is protected by God's power, which causes Grendel pain when he tries to approach it. This protection prevents Grendel from causing harm to the throne or to Hrothgar himself.
Other than brute strength, no weapons can pierce through Grendel's skin because he represents evil.