The speaker is looking back on his mother, and the poem begins with a small surprise: poetry has come into his hand after many years, and the only explanation he can find is "old world spirits" and the autumn light, which feels just like the light of his childhood. That light pulls his memory open.
What he remembers is spare and a little hazy. His mother wrote poetry, wore a scarf, and might have called herself Emily. He pictures her hair "lifted by iambic breezes," a gentle, romantic image. But he never saw her book, and the poem hints she found motherhood hard, while his father took naturally to being a parent.
The short, plain lines at the end carry the weight. "One day" repeats three times: she leaves home, then the country, then the world. The mood is quiet, wistful and unresolved. The speaker seems to admire her and miss her, yet he does not blame her or say how he feels outright.