What is a brief summary of the poem "The Listeners"?

"The Listeners" is a fairly accessible poem by Walter de la Mare.  The poem begins by telling readers that a traveler is knocking on the door of a lone house by a forest.  He arrived by horse, and it is nighttime.  The traveler knocks the first time, and nobody answers.  The traveler knocks a second time, and again nobody answers.  The poem then goes on to describe exactly how still and empty the house appears to be.  There is no explanation given as to why the house is empty or why nobody is answering the door.  The traveler then knocks on the door a third time, and nobody answers.  He then announces to nobody in particular that he came to the house as promised, but nobody answered.  

‘Tell them I came, and no one answered,   
   That I kept my word,’ he said. 

The traveler then mounts his horse and leaves.