Why is the sea a useful symbol? Does the sea comfort the speaker?

I think the sea is a symbol of loss and grief. Although some have interpreted the speaker’s grief as sadness over a lost lover, it probably reflects the feeling at any loss of a beloved person in death, like Tennyson’s dejection over losing Hallam.While the feeling here could involve merely the loss of a romantic relationship, it seems more poignant if the speaker has no hope for the return of the one who is lost. Without a death, there is no opportunity to connect the “hill” to a mounded grave, the “still” voice would be harder to interpret, and the “day that is dead” would be a weaker metaphor.