The epic poem Beowulf is unique in that the retelling of the poem is Christian, but the original version of the poem passed down through oral tradition originates from a pagan perspective.
Because symbols in literature are intended to represent something else meaningful to the reader/audience, the monsters in Beowulf are significant. The monsters inspire fear and cause great suffering, and from the point of view of the pagans, the monsters represent the fear of any dark threat that might interfere with the survival of the people. The monsters in Beowulf lurk in unexplored territories as well as outer edges of places that people might rarely venture; from these areas, real enemies appear, so the monsters in the poem also represent the unknown forces of danger that might come in the future.
From a Christian perspective, the monsters represent evil and separation from God. In the poem exists a direct allusion to the Bible, one that compares Grendel, one of the monsters, to Cain, the murderous brother of Abel. Cain killed his brother and was exiled from God as a punishment; according to the Christian retelling of the poem, Grendel is similarly deserving of spiritual rejection. Beowulf, as the slayer of monsters, is heroic in his Jesus-like decision to sacrifice himself for others in pursuit of the eradication of evil.
The monsters in Beowulf represent a number of abstract concepts. For the pagans who passed down the story of Beowulf orally, the monsters represented archetypal threats to the Germanic tribes who told the story. They were a common enemy that men needed to band together to defeat. The monsters were powerful and required a specific hero with wit and physical strength to defeat them. Beowulf had defeated a number of monsters before he came to Denmark to fight Grendel. These early defeats were necessary for Hrothgar to allow him to attempt the battle against Grendel in the first place. Therefore, they were archetypal challenges or threats to the Danes and Geats at the time.
When Beowulf was finally recorded in writing by Christian monks, the pagan version of the monsters were replaced by more traditional, biblical monsters that represented evil itself. Grendel is described by the poet as the seed of Cain. Beowulf can be considered a Christlike figure in this reading since he repeatedly saves the people from evil and even lays down his life to save them from the final threat from the dragon.
On a more metaphorical level, these monsters can represent Anglo-Saxon concerns with complex social and familial relationships. Grendel is jealous of the camaraderie of the Danes in the mead hall, so he attacks them. Grendel's mother attacks as a form of revenge for Beowulf's murder of her son. The dragon is protecting the treasure he guards at the end of the story. Here, the monsters can be viewed as expressions of man's struggle to find his place in the rapidly changing world.
The monsters can represent a number of concepts, depending on whether the perspective is pagan, Christian or humanistic.
The monsters in this poem can best be understood within the poem’s original pagan context and in the ways in which later generations attempted to make Christian sense of it. Grendel is defined as a descendant of Cain. In the Bible, Cain is exiled: he becomes somebody condemned to wander outside of the group he once belonged to. The same is arguably true of Grendel. He represents the fear we see in many Anglo-Saxon poems of being turned into an outsider. Grendel is jealous of the mead hall because he does not have recourse to a place of community like this. As such, he attempts to destroy it. Grendel is, we might argue, the ultimate example of what happens when behavior against social norms causes a man to be exiled for too long.
Grendel’s mother, in her own way, represents a subversion of societal expectations. In defending her son, she has behaved appropriately, but at the expense of attacking the greater group. As such she may represent the difficulties of balancing the various social expectations Anglo-Saxon society placed upon the community.
Beowulf, at least the modern translation, is written from a Christian perspective. Therefore, the symbolism of the monsters (Grendel, Grendel's mother, and the dragon) is that of evil. Since Beowulf is good, and on the side of God, that which is against Beowulf is against God.
Another view regarding the monsters is that they symbolize sin. Grendel, and his detest of the light (because he cannot live it it) symbolizes envy: "Then an evil creature who dwelt in darkness, full of envy and anger, was tormented by the hall's jubilant revel day by day." Grendel's mother symbolizes wrath (given her actions are fueled by the murder of her son). Lastly, the dragon symbolizes greed. It cannot fathom that one piece of its treasure is missing. Regardless of the vast treasure, the dragon must have the one piece which was taken.
One final definition of the monster's symbolism revolves around "the evil of human suffering caused by natural disasters" (taken from the eNotes Themes page on Beowulf). While the page denounces the accuracy of this idea, the symbolism behind the monsters in regards to human suffering has been defined previously.