Two people meet again, and something has changed. That is all Shelley gives us in the first line, "We meet not as we parted," and he never says what happened in between. We learn only that the speaker's "bosom is heavy-hearted," that the other person is "full of doubt," and that "one moment has bound the free." Leaving the moment unnamed is the poem's central strategy. What matters is its size: a single instant that splits a life into before and after, and that the speaker can neither undo nor stop mourning.
The second stanza tries to catch that instant in images, and every one of them is about vanishing. Lightning "flashed and died." A snowflake falls on a river, a sunbeam rests on the tide. Each is a small bright thing taken in by something larger and darker, and the stanza ends with shadows that "hide" it. The images grow gentler as they go. Lightning is violent, the snowflake melts silently, and the sunbeam is simply covered over. Loss here is not an explosion but a quiet erasure. Water keeps returning, first as river, then as tide, finally as the "briny dew" of tears, so that the speaker's grief seems to share the nature of what swallows the moment.
The third stanza names the cost. The moment is "singled" out of time "as the first of a life of pain," and the "cup of its joy was mingled," poured together with something bitter. Then comes the poem's most revealing phrase: "Delusion too sweet though vain." The happiness was false, and yet it was too sweet to give up. The speaker cannot wish it away, and cannot have it back, because it is "too sweet to be mine again."
In the fourth stanza he turns to address "Sweet lips" directly. The syntax is tangled, and the meaning is not fully clear. One reasonable reading is that if his heart could have hidden how completely "its life was crushed by you," the beloved would not have "forbidden / The death" he sought "in your briny dew." That is a startling idea: the speaker wanted to die in her tears, and something held him back. Such an extreme wish, set beside the restrained opening ("We feel more than all may see"), shows how much pressure has built up behind the polite surface.
The form works against this grief in an interesting way. Each stanza has five lines rhymed ABABB. The A rhymes are two-syllable, falling rhymes (parted/heavy-hearted, ever/river, singled/mingled, hidden/forbidden), and they sound like sighs. The B rhymes are single, firm syllables, and because the fifth line adds a third rhyme to the pair, each stanza closes with a thud: "free," "hide," "again," "dew." The lines have about three beats each, with unstressed syllables slipping between them, which gives a lilting, song-like movement. The poem sounds almost like a lullaby while describing a wound.
The text as given breaks off with a row of dots and then a final couplet: "Methinks too little cost / For a moment so found, so lost!" The couplet seems to say that death would be a small price for that moment. The rhyme of "cost" and "lost" binds payment to loss, and "found" and "lost" sit side by side in one line, so the reversal that the whole poem circles happens in a single breath. Whatever the reason for the gap in the text, the poem reaches its ending with something missing, which suits a poem about a moment that is gone.
The poem is worth reading for how much it does with so little information. Shelley is one of the great English Romantic lyric poets, and this piece shows the habit of turning private feeling into fleeting natural images such as lightning, snow and light on water. It gives no occasion, no name and no story. Instead it leaves the reader in the same position as the speaker, who can see only the shadow a vanished moment has cast over everything after it.