Theory:

Is there anybody there?’ said the Traveller,
Knocking on the moonlit door;
And his horse in the silence champed the grasses
Of the forest’s ferny floor: And a bird flew up out of the turret,
Above the Traveller’s head:
And he smote upon the door again a second time;
‘Is there anybody there?’ he said.
But no one descended to the Traveller;
No head from the leaf-fringed sill
Leaned over and looked into his grey eyes,
Where he stood perplexed and still.
But only a host of phantom listeners
That dwelt in the lone house then
Stood listening in the quiet of the moonlight
To that voice from the world of men:
Stood thronging the faint moonbeams on the dark stair,
That goes down to the empty hall,
Hearkening in an air stirred and shaken
By the lonely Traveller’s call.
                                     Walter de la Mare
Reference:
State Council of Educational Research and Training (2019). Term-1 English Standard-7. The Listeners by Walter de la Mare (pp. 42). Published by the Tamil Nadu Textbook and Educational Services Corporation.