Metaphor in Beowulf
To unlock one's word-hoard is a very common formulaic phrase in Old English or Anglo-Saxon used to describe a very formal, ceremonial speech. In answering the guard's question, the still unnamed hero of the Geats conforms to such expected conventions to explain his unexpected presence in Hrothgar's territory. In doing so, we not only learn more about the hero's respect for the customs of the land, but we also are able to see how eloquent of a speaker he is.
Jewel-giver is another kenning used for kings at the time, similar to ring-giver. The poet indicates that Hrothgar is pleased with Beowulf's resolve to help his people, and the atmosphere in the mead-hall turns festive.
The poet uses a feast as a metaphor for life, which would resonate with the audience. Note also how the poet does not describe this "fated place" as heaven or hell. Not mentioning some kind of life after death is odd for a Christian poet, but this is possibly an example of the pagan view of death taking precedence over the Christian view.