The tide rises(Longfellow 1). A new day awakens the nature and the starting of a new day.
It is almost night so "the traveler hastens toward the town."(Longfellow 1).
"The darkness calls the sea, with it's soft white hands."(Longfellow 2). It is now night across the sea.
"Efface the footprints in the sands." (Longfellow 2). The traveler is now gone and the sea erases his footprints.
"The morning breaks; the steeds in their stalls stamp and neigh, as the hostler calls" (Longfellow 3). Everything is waking up to the new day and ready to start.
"The day returns, but nevermore returns the traveler to the shore."(Longfellow 3).The day has started again and the traveler will never return to the shore, it's saying that we humans don't care for nature as much as we should.