When the horses first appear, Muir combines alliteration and expressive vocabulary to paint an initial impression of these newly arrived creatures.
a distant tapping on the road,
A deepening drumming; it stopped, went on again
And at the corner changed to hollow thunder.
Muir compares the horses that have appeared with legendary horses of the past, those used by knights or royalty long ago. The people beholding these horses are awed, perhaps intimidated at first by the creatures. "We did not dare go near them." However, Muir portrays the horses as having been sent on a mission to find and assist these people in their time of need, to reestablish patterns of friendship that had existed in past times but had been lost.
as if they had been sent
By an old command to find our whereabouts
And that long-lost archaic companionship.
Muir ends the poem by paying homage to the blessing of the horses-they are willing to work to help the humans and to make their life easier, but the humans remain very aware and respectful of the sacrifice being made by the horses. The comparison between the abandoned tractors and the horses reflects the power and the impact of their arrival.
Since then they have pulled our plows and borne our loads
But that free servitude still can pierce our hearts.
Our life is changed; their coming our beginning.