Nearly everything in Shelley's version of this ancient hymn is arranged to make one moment land: the instant a doomed ship is saved. The poem begins by calling on the Muses to sing of Castor and Pollux, the twin sons of Jove, born to Leda on Mount Taygetus. It then says what these brothers do: they are "the Powers who earth-born mortals save / And ships." The rest is a single scene that shows it. Sailors in a winter storm call on the Twins, and the Twins arrive. The central idea is that divine help meets human terror at its peak, and that fear, prayer and ritual can bring it.
The opening lines are crowded with compound epithets: "fair-ankled Leda," "Heaven-obscuring Child," "steed-subduing Castor," "snow-white lambs." These hyphenated labels are in the Homeric manner, and they give the start a formal, ceremonial weight, as if the poem were dressing the gods before presenting them. The names themselves are Roman, Jove and Saturn rather than Zeus and Cronus, which gives the translation an English-classical flavour. Even the Muses are "wild-eyed," which makes inspiration feel like a kind of frenzy, though that is a reading rather than anything the poem states. A small echo links the two halves: Taygetus is a "lofty mountain," and the terrified sailors gather on a "lofty prow." The high place of the Twins' birth quietly matches the high place from which the sailors call to them.
The most striking decision is syntactic. After the calm statement of lines 7–8, the poem launches a sentence that runs through the last fourteen lines, nearly two-thirds of the whole. It starts with "When wintry tempests," piles up the sailors' fear, their vow, their sacrifice, and the wave "bursting close behind," and holds back its main verb until the ship is almost under. Then comes the pivot: "The staggering ship--they suddenly appear." The dash acts like a gasp. The rhyme helps, too, because "bear" (the waters bearing the ship down) is answered by "appear," so disaster and rescue are tied together in the same sound.
The images of salvation are physical and bright. The Twins arrive "on yellow wings rushing athwart the sky," a streak of colour across a storm-dark scene. They then do two gentle things where we might expect violence. They "lull the blasts" and "strew the waves on the white Ocean's bed." "Lull" treats the wind like a restless child, and "strew" makes the sea sound like a bed being smoothed. "Mute tranquillity," with its long, soft vowels and its length, slows the line as the storm dies. Compare the harsh, clustered sounds earlier: "weltering waters," "staggering ship," "bursting." The ending is quiet. The sailors "plough the quiet sea in safe delight," and "plough" is a farmer's verb, suggesting that the sea, once a monster, has become a field they can work.
Shelley wrote in rhymed iambic pentameter couplets, and this is a real choice, since the Greek original is unrhymed. Rhyme gives the English a tidy, song-like finish, and it sometimes bends the language slightly. "Wind" has to be heard as it was in older poetry, to chime with "behind." "Sea" and "tremblingly" rhyme only if the last syllable is pronounced fully, which makes the word tremble a moment longer. The couplets also fit the story. Each pair snaps shut like a small wave, and a stormy sentence runs through them, pressing against the pattern until the final pair finally settles.
The poem's significance lies partly in what it preserves. The title credits Homer, because these hymns were traditionally attributed to him, although modern scholars generally doubt that. It also shows a Romantic poet turning an ancient religious song into English verse that keeps its force. Its picture of the divine is simple and moving: the gods here are not distant but come in answer to a cry, and the reward is the plain relief of the last lines, "from toil and dread / The sailors rest."