Not a single horse appears in these three lines, and there is no saddle, field or reins. What we get is a woman talking, a morning passing, and the way she walks. The title, "Rider", does the quiet work of telling us who she is. Everything else shows that identity leaking out of its usual setting. She is not on horseback, yet she is plainly still riding in some sense, carried by her subject. The central idea is that real devotion cannot be kept inside the activity that inspired it. It spills into speech, then into posture, then into the body itself.
The construction is spare. The poem has three lines of seven, three and five syllables, with no rhyme, no capital letters and no punctuation. It is close to haiku in its compression and in its habit of catching one observed moment, but it does not follow the 5-7-5 pattern. The short middle line is the most interesting departure. The poem also has no main verb. "Talking" and "a joy" both hang loose, with no "she is" or "she was" to anchor them. That makes the poem feel like an impression rather than a report, as if someone had glanced up and noticed these things before they could be arranged into a proper sentence. The observer is never named. Judging by the phrase "all morning", we might guess a listener who has been in the room long enough to see the pattern.
That phrase, "all morning", is the hinge of the poem. Without punctuation it can attach in two directions. Read upward, she has been talking about her horses all morning. Read downward, the joy in her step lasts all morning. The poem refuses to choose, and the ambiguity is useful, because it fuses the talk and the joy so they become one thing. There is also a small irony in the line's length. It is the shortest line, only three syllables, yet it carries the longest stretch of time. The poem takes a whole morning and passes through it in a breath, which suits a subject that, from the listener's point of view, might feel endless.
The word choices are modest but not careless. The possessive "her" appears twice, in "her horses" and "her step", and the repetition frames the poem so that the animals and the walking body belong to the same person, almost to each other. The sounds help. "Horses" and "morning" share the same vowel-and-r sound, so the two nouns echo across the lines and the animals seem to fill the morning. The word "joy" is the only named emotion in a poem otherwise made of concrete things, and it could easily tip into sentimentality. What prevents that is where it lands, in "step". The familiar expression is "a spring in her step", and swapping spring for joy names the feeling outright instead of letting an image show it. Still, the footing stays physical. One could even read a further layer into "step", since it is also a word that belongs to horses. This is an interpretation rather than something the poem states, but it suggests a woman who has begun to move like what she loves.
The poem's significance lies in how much it trusts what it leaves out. We are never told what the horses look like, what she says about them, or why she is so happy. Because the poem withholds the subject of her talk, it turns our attention to the effect of that subject on a person, which is perhaps the more truthful thing to notice. Most of us can recognise someone lit up by their passion, and most of us have been bored or charmed by an hours-long monologue about something loved. The poem catches the charmed version. It suggests that a morning of enthusiastic talk is not tedious but quietly beautiful, because you can see it in how a person moves.
For a student reader, "Rider" is also a good lesson in reading absence. Try changing the title to "Woman" and see how much of the poem's meaning disappears. The horses would remain, but the idea that she has become what she loves would be gone.