"Soeur Louise de la Miséricorde" (French for "Sister Louise of Mercy") alludes to a 17th-century French woman, Louise de La Vallière, who spent 13 years in King Louis XIV's court as one of his mistresses. She loved the king and was heartbroken and humiliated when he turned his attention to another woman. She eventually left for a convent where she became "Soeur Louise." This poem takes place in the aftermath of her relationship with the king.
She starts out by saying that she has been both subject to and the object of passionate desires. Now that her relationship has come to an end, however, her life is empty of passion, and "dust and dying embers mock" her metaphorical "fire." In other words, all the roaring passion she once had for the king has burned through her and nothing remains but the tiniest glow, which will soon be gone.
Bold repetitions make these opening lines feel both emphatic and desperate:
I have desired, and I have been desired:
But now the days are over of desire,
Now dust and dying embers mock my fire;
The balanced anaphora of "I have desired, and I have been desired" makes it clear that the speaker's passion was once reciprocated: she's been on either end of intense longings. There was a time when her life was full to bursting with love and sex, when she had little time for thinking about anything else. Epistrophe—the repetition of "desired"/"desire" at the ends of the first two lines—emphasizes the poem's central concern right from the start. And the repetition of "Now" draws the reader's attention to the speaker's present unhappy circumstances. She and the king may have once been gaga over each other, but that certainly isn't the case anymore.
The poem is made up of four quintains, or five-line stanzas. It is written in iambic pentameter, meaning lines contain five iambs (metrical feet with a da-DUM rhythm), as in:
I have | desired, | and I | have been | desired;
The poem's regular shape keeps on carrying poor Soeur Louise back to the same dreadful conclusion: desire is nothing but the "vanity of vanities," the greatest possible waste of a life.