The main theme of Beowulf is heroism shown through the transformation of Beowulf from a great warrior to a devout King. This involves far more than physical courage. It also means that Beowulf the warrior must fulfill his obligations to the group of which he is a key member as a thane. Beowulf's transformation is portrayed through three separate and increasingly difficult conflicts - with Grendel, Grendel's mother, and the dragon shows a clear division between Beowulf's youthful heroism as a warrior and his mature heroism as a reliable king.
There is also a clear-cut network of social duties depicted in the poem. The king has an obligation to behave with generosity. He must reward his thanes with valuable gifts for their defense of the tribe and their success in battle. This is why King Hrothgar is known as the "ring-giver." He behaves according to expectations of the duties of a lord when he lavishly rewards Beowulf and the other Geat warriors for ridding the Danes of Grendel. King Hrothgar's acts as king forsahdow Beowulf's manner of kingship in the second half of the poem. But the thanes have their obligations too. They must show undivided loyalty to their lord. Only in this way can the society survive and it also shows the importance of the relationship between lord and thane and expresses the ultimate value of that connection - social stability.
The battle scenes themselves are an indication of this change. The first battle is quick and seems to be a relatively easy feat for Beowulf, the second battle finds Beowulf needing weapons it order to triumph, and the final battle is almost like a sacrifice. He goes in knowing that he will probably die, and the scene is bloody and drawn out. Furthermore, Wiglaf enters the final battle to help him, showing the respect that he has earned from his thanes and that they are now willing to give their lives for him.
The tone of the poem is an indicator of the changes in Beowulf. In the first two battles there is an epic tone. Beowulf is gallant and described in a very physical sense. He is adorned in jewels by king Hrothgar and has the utmost confidence. By the final scene the tone is less bounding and more melancholy. Beowulf is less confident, and worries more about his people than his own reputation. The sadness in the tone also reflects the despair of Beowulf's kinsmen when he has died. This further relates the importance of the king to his people and the idea of mutual respect.
In his youth, Beowulf is a great warrior, characterized predominantly by his feats of strength and courage, including his fabled swimming match against Breca. He also perfectly fulfills his social obligations. He has the virtues of a civilized man, as well as the strength of the warrior. He looks after his people and is always gracious and kind, but as with any hero Beowulf does have some flaws. His defeat of Grendel and Grendel's mother validates his reputation for bravery and establishes him fully as a hero - it is here we first see a little flaw. Beowulf seems to have too much pride in himself though. Initially it is said that Beowulf goes to fight Grendel because, he has defeated giants and sea-monsters so he figured he should try to fight Grendel at least once. As a typical trait of a hero, Beowulf is concerned with his reputation, and thus volunteers to terminate Grendel for nothing more than the glory of doing so. Beowulf states, "this was my determination in taking to the ocean.../ that I should once and for all accomplish the wishes / of your adopted people, or pass to the slaughter, / viced in my foes grip (632-636.)" Even with the enormous amount of confidence Beowulf possesses, he understands that fate will work its magic no matter what and he could be killed at any point in his life. He faces that reality by showing no fear and preparing for a positive or a fatal outcome.
When the mother attacks Heorot, Beowulf runs after her and while all of the other warriors exhibit cowardice, Beowulf, being courageous, simply jumps into the depths of the other world to defeat her. This is also another characteristic of the hero, he selflessly crosses a boundary in order to protect social stability, not caring if he dies or not. This battle seems somewhat transitional as Beowulf is unable to defeat the mother with his bare hands. In fact, his sword doesn't even get the job accomplished, and Beowulf is almost killed. By some fantastic notion a giant's sword magically appears and Beowulf is able to defeat her at last. Perhaps through relying on tools to help defeat the mother, Beowulf is stepping towards being able to have more a more wise mind instead of a glory seeking one. This shows Beowulf's transition into a more profound part of his life and from here out his life will get decidedly more difficult.
Mutual love and loyalty is seen when Beowulf's transition from warrior to king is complete in the second half of the poem. In particular, his final battle with the dragon, portrays the difference between the duties of a heroic warrior and those of a heroic king. Beowulf does not fail his people, even at the last, when as an old man he goes forward without hesitation to battle the dragon. He does what he knows he must do. In the end he fights the dragon more for the good of his people than for his own pride; he dies relieved because "I should have been able to acquire for my people / before my death-day and endowment such as this (2794-95)." This scene shows Beowulf's sapienta et fortiudo, in that he recognizes that something must be done in order to stop the attacks on his people and to maintain social stability, and having the courage to act on it knowing he might die. However, even though he seems to be acting selflessly, there is also a reminiscence of his glory-seeking youth because he wants the treasure to be taken from the dragon's lair. Simply saving his people isn't enough. It seems he is aware of the heroic paradox that he will be glorified in life or death for his actions.
After the final battle there is another expression of the importance of loyalty in their culture. That is when the thanes that left Beowulf "bore their shields ashamedly (2847)." It is the ultimate disgrace that they left their lord, because the lord is their source of livelihood and a thane is expected to willingly give his life for his provider. Wiglaf sums up this tie when he says, "death is better / for any earl than an existence of disgrace" (2887-88), meaning that the bond between lord and thane is so strong that it is better to die than to disgrace that relationship. His thanes revere him in the final lines, "they said that he was of all the world's kings / the gentlest of men, and the most gracious, / the kindest to his people, the keenest for fame" (3178 - 3180).
The poem ultimately shows the importance of a leader that is adorned by his people. The relationship between Beowulf and his people at the end mimic one in which the leader gives to the people by supporting and defending them and they give in return by revering and serving him. The value of his authority, then, is at least as great as any social contract that we might have today; it is one in which the ties are bound by a need to survive and are drawn from a deep mutual love and loyalty.