Keats opens with a declaration of national happiness, then undermines it in the same breath. "Happy is England! I could be content" sounds like a patriotic announcement, but the second half of the line is a conditional. The speaker is describing a contentment he *could* have, which tells us he doesn't quite have it. The rest of the sonnet shows how far he is from it.
The poem is built as a pair of attempts that both fail. Lines 1–4 praise England: its "verdure," its breezes blown "through its tall woods with high romances blent." That last phrase suggests the woods are thick with old stories as well as trees. Then "Yet" arrives in line 5, and the mood turns to "a languishment / For skies Italian." The second attempt begins at line 9 with the same words, "Happy is England," this time about its "artless daughters," and the second "Yet" in line 12 brings the same reversal. The repetition makes the pattern feel like a habit of mind. He tries to settle for what he has, and his imagination won't let him.
The wording of the two longings also escalates. In the first he "sometimes" feels a languishment, a limp, almost sickly word. In the second he "often" burns "warmly." The feeling has grown more frequent and more physical. The "inward groan" of line 6 is private and half-suppressed, as if he is embarrassed by the wish. And the fantasy is grand: to "sit upon an Alp as on a throne." The English landscape is gentle and enclosed. The Alp is lofty and solitary, a seat above everything. From there he would "half forget what world or worldling meant," so the wish is to escape ordinary life and not just to travel. The word "half" is honest, though. He doesn't claim he could forget it completely.
The form adds to the tension. The octave rhymes *abba abba* (content / own / blown / blent, then languishment / groan / throne / meant), which is the Petrarchan pattern. That is an Italian sonnet design, so a poem praising England is built in a form from the country it desires. The sestet rhymes *cdedec*, a looser pattern that ends without a tidy couplet. The meter is iambic pentameter, but the first line starts with a stress on "HAP-py," and the feminine endings of "daughters" and "waters" give the later lines a soft, trailing quality.
The women of the sestet are described in the same terms as the English landscape. They are "artless," their loveliness is "simple," and their "whitest arms" cling "in silence." Silence and simplicity are meant as compliments, but "Enough" is repeated twice, and the word tends to give away that something is missing. What he turns to next is "Beauties of deeper glance," and, importantly, "their singing." Silence is set against song, and plainness against depth. Judging by the imagery, "deeper glance" suggests more mystery and experience than the English girls offer, though the poem never says so outright. The tone is a little condescending toward the English women, and a modern reader may notice that neither group is given any voice of its own.
The last line gives the speaker's real wish: "And float with them about the summer waters." After the heavy "Alp" and "throne," the language turns liquid. "Float," "summer," and "waters" are all soft, open sounds. The fantasy has moved from power and solitude to drifting in company, which is a more relaxed idea of happiness. The poem ends on the dream and never returns to England.
The sonnet matters because it is honest about divided feeling. Many poems of national praise stay loyal to their subject, but this one admits that affection for home can sit beside a restless appetite for somewhere else, and the "yet" in each half keeps the two in balance. It also shows how much meaning a small word can carry. "Could" in line 1 and the rising "sometimes" to "often" tell the whole emotional story. Keats died in Rome in 1821, which gives these lines an irony in hindsight, but the poem doesn't need that fact. Anyone who has loved a place and still wanted to leave it will recognize the mood.