De La Mare creates a very eerie and tense mood in The Listeners. The overall meaning of the poem is up to the interpretation of the reader. You have a traveler who visits a house where we presume he knows the occupant. However, his words are only heard by a group of phantoms or ghosts.
Setting, as always, helps create the mood. It's dark, in a forest, at a medieval or gothic castle/mansion (the place has a turret). He uses descriptive words and phrases like "moonlit door," "leaf-fringed sill," "faint moonbeams on the dark stair,"empty hall," and "shadowiness of the still house." These descriptions offer an imagery that is very tense and spooky, and possibly supernatural. The traveler is also alone and confused. This gives the reader a similar feeling of concern.