The traveller could be used as an analogy for what?

The capitalization of Traveller is an indication of some unknown and unidentified mythic importance. The only thing we know about him is that he made a promise to come to this home, and kept his word. He arrived by horse, and when his knocks bring seemingly no physical response, he appears to be invested with keen powers of intuition: he very strongly senses the presence of the listeners inside the house despite their silence and stillness. That intuitive awareness also brings the assurance that any further attempts to gain entry will be fruitless. Before taking his leave, he appeals to the listeners to deliver a message to some unidentified “them.” The message is that he kept his promise by showing up, but no one came to greet him so he left.