In the epic poem Beowulf, how do Beowulf's heroic qualities affect the story?

In the epic poem Beowulf, Beowulf's heroic qualities are essential to the progression of the plot. His heroism sets up the major battle scenes and conflicts of the poem.
Near the start of the poem, Beowulf has heard that the monster Grendel is terrorizing Hrothgar's kingdom. Grendel is angered by the sounds of celebration in the mead hall at night and goes to the hall to kill and eat the men who are feasting there. This continues for some time, and no one seems able to stop it. Beowulf decides to go to Hrothgar's kingdom with his own men to try to defeat the beast. Beowulf is granted permission by Hrothgar and eventually succeeds in killing Grendel. This choice, to cross the sea and go to a foreign kingdom to help a king he does not even know personally only to put himself in physical danger to fight the monster, shows Beowulf's heroism: he puts his life on the line to save others.
Later, Beowulf travels to the monster's cave to kill Grendel's mother, who has continued to stalk the kingdom to avenge her son's death. Beowulf is brave: he decides to go to the monster's home turf, so to speak, and take her on. He is helped by a magical sword, and Beowulf does defeat the beast. This ushers in a period of peace for Hrothgar's kingdom. 
Later, at the climax of the poem, Beowulf is an old king whose people are being threatened by a dragon. Even though he is old and somewhat out of practice, our hero puts himself on the line again to save his people. He is mortally wounded in the fight, but one of his men steps up and kills the dragon. Beowulf's heroism is celebrated by his men, who build him a monument and an impressive funeral pyre. 
In conclusion, Beowulf's heroism moves the plot along and sets up the major conflicts/battles in the poem. His heroism is also a key feature of epic poetry, which helps to define Beowulf as such.