"Flushed with victory he groped his way, a brave young warrior, and suddenly saw piles of gleaming gold, precious gems, scattered on the floor, cups and bracelets, rusty old helmets, beautifully made but rotting with no hands to rub and polish them. They lay where the dragon left them; It had flown in the darkness, once, before fighting its final battle. (So gold can easily triumph, defeat the strongest of men, no matter how deep it is hidden!) And he saw..."
What theme do the lines (from Beowulf) suggest?
The lines in question from Beowulf illustrate the themes of glory and loyalty. The lines describe Wiglaf's traverse into the den of the dragon. Beowulf has ordered Wiglaf into the den to bring back the hoard of treasure for Beowulf to look upon before he pass from the earth (dies).
Wiglaf's loyalty to Beowulf insures that he (Wiglaf) will empty the den of its treasure: "Then I heard that a single man emptied the hill of its hoard of giant-craft." Wiglaf insures that he brings out every single treasure for Beowulf to gaze upon. Beowulf wanted to insure that his people were taken care of after his death, and the dragon's treasure will insure this. Wiglaf could, since he is alone, take the entire hoard for his own. His loyalty to his lord (Beowulf) insures that he does the right thing.
The lines in question also illustrate the glory of the win in battle. Since defeating the dragon, the dragon's treasure becomes the Geats. Since being named the new king, the treasure falls to Wiglaf. Outside of this, Wiglaf understands his duty to God (since being trained well by Beowulf). Wiglaf knows that battles should be fought for the glory of their gods (in this case, both Beowulf (god) and God (the Christian God).