De La Mare's "The Listeners" is interesting because, while the Traveler himself is the first person described in the poem, the point of view is ultimately that of the titular Listeners inside the dark house. At the end of the poem, "when the plunging hoofs were gone," the Listeners are still there, absorbing and interpreting the scene through its sounds.
Because of this focus on the Listeners, de la Mare uses sound-based details to set the scene throughout the poem. We, as the reader, imagine the scene through the interpretation of these details, just as the Listeners do. The Traveler's voice in the quietude, the sound of him "knocking on the moonlit door," the way his horse "champed the grasses" as he waited for his master, and the heavier sound of the Traveler's knock as he "smote" a second time—all of these elements indicate to the Listeners that the Traveler has arrived. In the same way, then, the sound details at the end of the poem are what indicate to the Listeners that the Traveler is departing. They heard, first, "his foot upon the stirrup," which signifies that he is climbing back onto his horse in readiness for departure. The next sound, that of "iron on stone," is the sound of the horse's iron horseshoes striking stone, perhaps the stone of a courtyard or of an old road, now little used. This sound indicates to the Listeners that the Traveler is leaving them, having, as he says, "kept my word."