Let's be even more exact and call this theme "Nymph and the Natural World." We've got an Oread commanding the sea to whirl up and meet the land (especially the forest). While we don't know if the sea ever actually does as the Oread tells it, we can't deny that this nymph is one powerful chick—her language is intense and demanding, and the sea practically becomes the land in her language. The humanlike creature thus has some real power over nature in "Oread."
The nymph has no hope of controlling the sea, and the land and sea can never be merged. This poem was doomed from the get-go.
Um, hello, our Oread is the most powerful nymph ever. (Just look at her words!) The sea will surely do as she commands.