Shelley never says who the "––" in the title stands for. The blank stays blank, and we are left with a "thou" who has "soft eyes" and a speaker bargaining with loss. Almost everything in the poem is conditional. "If tenderness and truth could last," he begins, then "I should not weep." The rest follows the same pattern of wishes: "It were enough," "Couldst thou but be." None of them is granted.
What he asks for is surprisingly modest. Passion is a "trance," something feverish and dreamlike, and the poem assumes it will pass. He hopes only that the quieter pair, tenderness and truth, might survive while the "wild feelings" lie in a "mortal slumber, dark and deep." "Mortal" does double work here. It makes the sleep human, but it also brings it uncomfortably close to death, as if the feelings might not wake. Even so, he wants little: to see "Thy soft eyes gazing tenderly" and to "dream the rest." Imagination will fill in whatever is missing, as long as the beloved stays constant. The most striking image is his picture of himself as the "secret food of fires unseen," fuel for a flame nobody can see. Love here is hidden and self-consuming, and the speaker seems willing to be consumed.
The third stanza turns to nature, and it picks up a word from the first. The "slumber" of dead feelings becomes "the slumber of the year," and the echo sets up a comparison. Winter's sleep ends reliably: "The woodland violets reappear; / All things revive in field or grove, / And sky and sea." Then comes "but two." On the most natural reading, everything revives except two things, which "move / And form all others, life and love." If so, life and love are not seasonal like violets. They are the forces behind the whole cycle, and nothing guarantees their return. The syntax is slippery enough that a reader could take the lines differently, and that uncertainty adds to the ache. The violets are the poem's only concrete image, set against a run of abstractions (passion, tenderness, truth, life, love). That makes the contrast between nature's dependable renewal and human feeling's fragility feel small and personal rather than grand.
The form supports this. Each of the three stanzas has five lines, mostly in light iambic tetrameter: "When passion's trance is overpast." The eight-syllable lines have a songlike simplicity that keeps the emotion quiet. The rhymes bunch up in an unusual way. In the first stanza "keep," "deep" and "weep" are three rhymes in a row, and the stanza ends by repeating itself: "I should not weep, I should not weep!" That can be read as reassurance, or as someone repeating a claim to convince himself. In the second stanza "see," "tenderly" and "be" chime together, and "unseen" and "been" pair up as long as "been" is pronounced to match. The sentence "Couldst thou but be as thou hast been," ends on a comma and never finishes. The stanza break becomes a silence, and the wish trails off into the violets. In the last stanza "grove," "move" and "love" look like a rhyme on the page but do not quite agree when spoken aloud, so the poem's final word lands on a sound that does not fully settle.
What makes the poem worth reading is how much it does in fifteen lines. It has no story, no named people and no scenery beyond a few flowers. It gives only the shape of a feeling: the hope that something gentler might outlast the fire, and the fear that nothing promises it will. The "if" and "couldst" never resolve into "is." By setting the sure return of spring beside a love that cannot count on the same return, the poem makes a very ordinary sadness feel exact.