This is one of Sor Juana's love sonnets, and probably the best known of them. It was printed in Inundación castálida (Madrid, 1689), the first volume of her work to reach print in her lifetime, among the pieces the old indexes described as written "at the prompting of a feeling."
The whole sonnet is a single idea carried to its end. The beloved is absent; what remains is his image — the shadow, the illusion, the fiction — and it is that image she addresses. The two quatrains ask it to stay and reproach it for seducing only to flee; the tercets turn around and deny it the victory: you can escape the embrace, but not the mind that holds you.
It is a classical sonnet, fourteen hendecasyllables in two quatrains and two tercets. The stanza moves like an argument — thesis, objection, reply — and closes on the line everyone remembers: if the body can keep no one, the imagination can. The conclusion does not console; it turns loss into a willing prison.
The verse is kept in Spanish. Translating it in passing would replace the work with a paraphrase of it.