Along with Grendel, Unferth represents the theme of envy in the epic. Shortly after Beowulf's arrival, Unferth, full of mead, insults the guest at a banquet. This is more than an awkward moment for the hosts. Unferth's behavior goes against the code of hospitality. Unferth accuses Beowulf, as a lad, of entering a dangerous, foolish seven-night swimming match on the open sea against a boy named Breca — and losing.
Fortunately for the Dane, Beowulf demonstrates a noble spirit as well as ease with language as he refutes the charge and puts Unferth in his place. In fact, Beowulf says, he swam with Breca for five nights, not wanting to abandon the weaker boy. Rough seas separated them, and Beowulf had to kill nine mighty sea monsters before going ashore the next day. Beowulf points out that Unferth's fame lies mainly in the fact that he killed his own brothers. If the Dane could fight as well as he talks, says Beowulf, King Hrothgar might not have such a problem with Grendel.
Unferth later admits Beowulf's superiority after the defeat of Grendel and lends him a treasured sword, Hrunting, for the battle with Grendel's mother. While the sword is ineffective, at least the Dane is making an effort. We might suspect that Unferth's character flaws will surface again, but he has been humbled and his character improved for the purposes of this story.