In Beowulf, Grendel represents disorder, miserable solitude, and fierce hatred, and he stands in contrast to the ordered world of the mead hall where the king and his warriors all know their place.
The poet tells us that Grendel is an “enemy in hell” who disrupts the peace and happy joys of Heorot. Within Heorot, all is orderly and right. Hrothgar sits upon his throne and gives treasure, food, and drink to his loyal warriors, who in turn give him their allegiance and support his cause in battle. This is how the world should be in this culture. But when Grendel steps onto the scene, all of this order and peace falls apart.
Grendel is a “fierce spirit” and a “waste-wanderer.” As a descendent of Cain, he is an outcast from human society, and this fills him with envy and hatred. He sees the joys of the mead hall and despises them because he cannot take part in them. He lives in exile and banishment, and he becomes “savage and cruel” and greedy. In his hatred, he decides that he will break the order and peace and joy of Heorot, so he enters the hall at night when the warriors are sleeping, and he kills and eats many of these men.
The violence does not end there. Grendel comes back again and again, and there is nothing Hrothgar and his warriors can do to stop him. Their world is completely disrupted and disordered. The joy and companionship that should dominate the mead hall are broken, and the men mourn their murdered comrades.
If the mead hall stands as a symbol for the world, then Grendel is certainly the element of disorder that enters into that world and turns it upside down. It takes a hero like Beowulf to set things right once again.