In The Listeners, why does the traveller say "Tell them I came, and no one answered, that I kept my word"?

The closing words of the traveller become the central
point of the poem.  De La Mare seeks to build a sense of "wonderment" in the reader. 
This means that the reader is so much a part of what is happening and what is
experienced that they formulate questions that are within the context of what is
transpiring.  To this extent, the traveller's words cause us to wonder and simply not be
able to fully explain why he says what he says.  The traveller says what he says in
order to demonstrate a certain level of certainty that clashes with that of uncertainty
and a lack of clarity.  The traveller represents a force of totality in a world where
ambiguity is present.  In the end, the traveller does "keep his word" and does represent
a type of constant.  Yet, De La Mare places this in context, for while human beings
might wish to display some level of control and absolutism about what is happening
around them, the reality is that he is outside of the norm.  The world in which the
traveller visits is one of uncertainty.  The "phantoms" and "listeners" abound in this
world, making the role of the traveller an aspect of the larger whole.  In the end, when
he rides off, the reader is left to question his role in the affair as well as the
entire condition, in general.  The best one can do at the moment is to understand that
there is some unexplained force that brought the traveller to this point, to force him
"to keep his word."  Yet, while this is done, it does not eliminate the profound sense
of the unknown that grips everyone involved.  It is for this reason that the words that
the traveller says is not as important as the entire atmosphere created, something that
the traveller, like it or not, is a part.