"The Emigrée" opens with a mysterious first sentence: "There once was a country..." Immediately, this tells the reader a lot about the rest of the poem. First of all, this phrase alludes to the typical opening of a fairy tale ("once upon a time"). The poem has a fantastical, dream-like quality running all the way through—and this line helps set that up.
Pushing this idea further, this also means that the reliability of what follows is under question from the beginning. That is, when the speaker presents the deep love that she holds in her memory for her home country, the poem subtly questions how much of this memory is real and how much imagined.
This opening phrase also gently subverts the typical fairy-tale opening by focusing on a place (rather than a time), demonstrating that the speaker's identity—as an emigrant from one country to another—is largely defined by where she lived as a child and where she lives now. Finally, the ellipsis caesura that follows this opening remark makes the fairy-tale statement trail off, indicating it is somehow interrupted or incomplete. Subtly, this hints at the way that the speaker's life itself suffered a kind of rupture when she had to leave her home.
After this caesura, the speaker clarifies which country she is talking about—the one in which she was born and, for a time, raised. She tells the reader how she was forced to leave when she was a child but that her memory of her home city remains strong and clear. The discussion of the memory thus begins an important relationship between memory and light that runs throughout the poem, with light representing warmth, knowledge, and moral goodness.
Lines 2-4 ("but my memory ... the mildest city") are also deliberately vague, the speaker explaining how it "seems" she never saw her city in "that November" which she is "told" visits itself upon "the mildest city." There's a lot of second-hand information here ("seems" and "I am told"), and it's not quite clear what is being discussed. Perhaps the speaker is referencing a particular November—maybe the one in which war took hold of her city—or maybe she is talking about Novembers more generally. Is November meant to represent the coming winter, and, metaphorically, times of death and hardship? Is "the mildest city" her home city, or just a turn of phrase?
It's hard to say, but this is in keeping with the way the poem never offers much in terms of specifics about the speaker's situation. Most likely, this is intended to make the poem more universal, looking for common ground in the emigrant experience.