Keats begins like a man emptying his pockets after a long day: "Many the wonders I this day have seen." What follows is a tour of sunrise, sunset, sea and moonrise, a whole day compressed into thirteen lines of marvels. Then the last two lines turn the poem upside down. All these wonders, he says to his brother George, would be worth little "without the social thought of thee." The central idea is simple and warm: beauty is not complete until it is shared, and even a solitary walk is made richer by the person you want to tell about it.
The poem is a sonnet, but a slightly mixed one. The first eight lines rhyme *abba abba* (seen / tears / peers / lean, then green / fears / hears / been), the pattern of the Italian sonnet. The final six lines, however, run *cdcd ee*, closing with a rhyming couplet in the manner of Shakespeare. That blend suits the poem's shape. The octave piles up what Keats has seen, and the sestet brings it back to George. The turn arrives at line nine with "E'en now, dear George," a sudden shift from looking at the world to speaking to a person. The meter is a flexible iambic pentameter. The opening line starts with the stress on "Many," which gives it an urgent, exclaiming energy before the rhythm settles.
The imagery is where Keats shows off. He makes the natural world a cast of characters. The sun "kissed away the tears / That filled the eyes of Morn," so the dawn is a weeping figure and the sunrise a tender gesture. The tears are probably dew, though the poem never says so. Evening clouds become "laurelled peers" who "lean" from "feathery gold," a picture of crowned, noble figures looking down from a balcony of light. "Peers" suggests both equals and aristocrats, and laurel is the traditional crown of victors and poets. The sky is a courtly gathering.
The ocean gets a different treatment. Instead of personifying it in one image, Keats lets it swell through repetition: "its vastness, its blue green, / Its ships, its rocks, its caves, its hopes, its fears." The repeated "its" works like waves arriving one after another. The list also slides from physical things (ships, rocks, caves) to emotions (hopes, fears), as if the sea holds human feeling as well as water. By the next lines it has a "voice mysterious," a slightly archaic phrase with the adjective placed after the noun, which makes it sound older and more solemn. Anyone who hears it "must think on what will be, and what has been," so the sea becomes a prompt for thinking about past and future.
The sestet shifts from grand to intimate. Cynthia, the old poetic name for the moon, is "peeping" from "silken curtains," and the language becomes playful and almost mischievous. She shows herself so "scantly" that it seems "her bridal night," with "half-discovered revels." The moon is a shy bride half-glimpsed through her bed-curtains. Notice the changing scale. We began with the enormous ocean and now end on something small and secret. The poem has also moved through a whole day, from morning through evening to night, and from sky to sea and back to sky.
The closing couplet is a rhetorical question: "But what, without the social thought of thee, / Would be the wonders of the sky and sea?" It echoes the opening word "wonders" and so closes the circle, but it changes the meaning. At the start, wonders were things Keats had seen. At the end, they depend on a relationship. "Social" is a good choice of word, because it suggests companionship as the thing that gives experience its value.
That is what makes the poem worth reading. It has the sensuous, personified nature description that readers look for in Keats, but it refuses to leave nature as the final subject. Beneath the gold clouds and the bridal moon, the poem is a piece of affection, a verse letter in sonnet form. It suggests that wonder looks outward as well as inward, and that the instinct to say "look at this" to someone you love is part of seeing well.