The poem begins with a small word that makes you feel you have walked in halfway through a thought: "Or, from that Sea of Time." Judging by that "Or," Whitman is offering one more picture of where his writing comes from, and this one is a beach. His poems are the "Spray" and the "double winrow-drift of weeds and shells" that the tide leaves in lines along the sand. They are things the ocean of time has pushed ashore, and Whitman casts himself as the one who gathers them rather than the one who carves them.
The central image turns on a paradox. The shells are "limpid-cold and voiceless," yet the speaker is sure that held to the ear they will bring up "Murmurs and echoes," "Eternity's music, faint and far." The phrase "tympans of temples held" is a neat double meaning. Read literally, shells are pressed to the eardrums at the sides of the head, but "temples" also hints at sacred buildings, so listening to a shell becomes almost a religious act. The sound travels "inland" from "Atlantica's rim" to reach "the Soul of the Prairies," so the poems carry the voice of the whole ocean into the middle of the continent. Whitman calls their message "old, yet ever new and untranslatable," which admits that what a poem offers can't be turned into plain explanation. You have to hold it to your ear.
The poem's modesty and its ambition sit side by side. Whitman calls his work "Infinitessimals out of my life, and many a life," tiny scraps, "waifs from the deep." But the parenthesis that follows is generous to the point of recklessness: "not my life and years alone I give—all, all I give." The doubled "all" sounds like someone emptying his pockets onto the sand. The words "cast high and dry" suggest the poems are stranded, left for whoever walks by, and the section ends on its shortest line, "Wash'd on America's shores." After the long, rolling lines, that brief line works like a wave drawing back.
That rolling quality is the poem's real music. There is no rhyme and no regular meter. Instead the lines lengthen and shorten like surf, and the sound is packed into hyphenated compounds such as "curious-convolute" and "limpid-cold." "Convolute" means spiralled, like the shell itself, and the word twists as it is spoken. The exclamations and the address ("O little shells") give the voice a tender, almost cooing tone. The parentheses act like small eddies, pulling the reader aside to think before the main current resumes.
The second section drops nearly all grammar and gives only a pile of noun phrases: "Currents of starting a Continent new, / Overtures sent to the solid out of the liquid, / Fusion of ocean and land." With no main verb to hold them together, they read like another heap of wrack, things set down side by side. The idea is that a new continent, and a new kind of poetry, is being made where liquid meets solid. The sea sends "Overtures," which suggests the opening of a piece of music, and the land receives them. The poems themselves seem to join this fusion, since they are fluid, flowing lines that end up as solid objects on a page.
The last lines change the mood. The waves have been "tender and pensive," but the parenthesis admits they are "Not safe and peaceful only—waves rous'd and ominous too." The tide that brings shells also brings "Death's waves," and the sea comes "Raging over the vast, with many a broken spar and tatter'd sail." The wreckage of ships gathers in the same drift as the shells. "Who knows whence?" admits that nobody can say where this force comes from. It is a surprisingly dark ending for a poem that began with gentle murmurs, and it keeps the beach picture honest.
The poem is worth reading for how it describes poetry's job in a young country. Whitman links America's coastline to its interior and ties a new nation to something as old as "Eternity." He does not claim to be creating a monument. His songs are what the sea of time has left, and they carry both its music and its danger.