Shelley opens with a challenge rather than a statement. "Why is it said thou canst not live / In a youthful breast and fair," he asks, speaking to Love as if it were a person who could answer back. We never learn who is doing the saying. The poem simply sets a common doubt against its own conviction. The reply comes at once and carries the central idea: Love can "eternal life give", so it cannot itself be mortal. Pain, age and even death fail to touch it, and it keeps its "unchanging bloom, / Fixed tranquil, even in the tomb."
The imagery behind that claim is quietly botanical. Love is never called a flower, but the vocabulary insists on it: "bloom", "dew", and above all the "vermeil hue", a rich vermilion red. Against that colour the poem sets "blanch", the whitening of age and death. Dew should freshen a petal, yet here it is death's "poison dew", and the flower is still unharmed. The syntax is knotty in these lines, but the sense seems to be that death, "time's dread victor", has to admit it has no power here. The first ten lines are also tightly built. Two alternating-rhyme quatrains (live/fair/give/there, then possessed/hue/confessed/dew) lead to a closing couplet. That couplet fastens "bloom" to "tomb", so the rhyme itself argues that life and grave cannot separate love from its freshness.
Then comes "And oh!", and the poem changes method. Up to this point it reasons ("Since… Since…"). Now it appeals to experience. Love arrives as a sunrise, the "day-star" that finds the soul "reviving", with every energy "more vivid" and soaring. Resurrection language is attached to an emotional moment, so love seems to bring the dead part of a person back to life. The next image is gentler: a "rapturous thrill, / Like June's warm breath", flying "athwart" the mind and stealing "O'er each idea". "Steal" is a good choice, since this love does not storm the mind but slips in. The phrase "When other passions die" quietly separates love from every other feeling. Other passions burn out, but this one belongs to a different order. The rhymes loosen here too. "Thrill" and "steal" only half match, and the music seems to relax along with the feeling.
The ending is the most striking part. The long question ("Hast thou ne'er felt…") drifts into a landscape: a "wild noonday dream" beside a "lonely stream", where "Silence says, 'Mine is the dell'". The idea is paradoxical, since silence speaks and rules like a monarch whose "silent reign" no "murmur" or "echo" disputes. Notice that the stillness is built from negatives, "not a murmur… not an echo", so we hear the place by what is missing. It also echoes the earlier "Fixed tranquil, even in the tomb". The grave and the dell are both defined by calm, and the poem hints that love's deepest home is a hush rather than noise. The last line is short, and it never answers the question it grew from. The poem ends on a held breath instead of a conclusion.
The rhythm supports this. The lines are mostly iambic, lilting and song-like, and some alternate longer and shorter lines, which gives the opening a light, questioning bounce. Toward the end the lines settle into slow, even beats, and the reader slows down with them.
The poem's diction is conventionally poetic: "vermeil", "athwart", "dell", "fell". Its images of flower, dawn, breeze and stream are familiar ones rather than startling inventions. Its interest lies elsewhere. It shows a Romantic habit of thinking: love is a spiritual force that outlasts the body, and nature is where such feelings can be sensed. It also shows how a poem can move from debate to atmosphere. It begins by arguing with a doubter and ends by letting stillness make the case instead.