The poem follows a loose narrative. In the first stanza, natural images overshadow the sorrow of humankind. In the second, a figure with "red mournful lips" arises, seeming to carry with her the weight of epic tragedy. She moves into the natural world, and the images that seemed sufficient in themselves - the sparrow, the moon - now express the infinite sadness of human misery.
This poem was written in 1891, only two years after Yeats met and fell in love with Maud Gonne. Yeats uses two classical allusions in the highly structured poem, one comparing the woman's doom to Odysseus, who helped in the expedition to recover Helen when Paris took her from Sparta. He only returned after ten years. "Proud as Priam" refers to Paris's father, who was killed by Achilles's son, Neoptolemus, after the fall of Troy.
Before the woman's presence in this poem, the world exists apart from humankind. It's natural beauty and struggle "blot out" the more complicated struggles of humankind. The influence of the mournful woman, though, invites human meaning into the poem. First, the woman inspires the poet with epic comparisons; then, when she moves out into nature, she recasts the moon, sparrow and leaves in terms of human sorrow.
Yeats thus suggests the inspiring, albeit sorrowful, nature of love - both in terms of a particular beloved and in terms of the feminine in general. The beautiful woman does not "compose" the natural elements around her, but her influence renders them incapable of expressing any meaning other than that of humankind. Whether the woman stands for Ireland, for Maud Gonne, or for the spirit of the feminine, she redefines the force of the world, focusing it into an expression of human sorrow.