Winter is where poets usually go to mourn, but Keats's December is oddly cheerful. The tree and the brook in these "Stanzas" are both called "too happy," and not because the weather is kind. The north wind sends a "sleety whistle" through the branches. They are happy because they cannot remember the summer they have lost. The poem is about the mercy of forgetting, and about the sad fact that people are not given it.
The first two stanzas are built as twins. Each opens with the same line, "In a drear-nighted December," then turns to address something in nature, and each insists that it "ne'er remember[s]" what came before. The imagery is precise. The tree's lost summer is "green felicity," so greenness and happiness are one thing. The cold fails to "undo" the branches, and even the "frozen thawings" cannot "glue them / From budding at the prime." That phrase is a nice piece of invention: it pictures a thaw that refreezes, a sticky winter mess that still cannot hold back spring. The brook's summer is "Apollo's summer look," as though the sun-god had once gazed down at it. Now the water has stopped its "crystal fretting." "Crystal" gives us the ice, while "fretting" makes the bubbling sound like nervous worry. Then comes "petting," which means sulking. Judging by that word, Keats imagines the brook as a child who might have pouted about the loss but sweetly doesn't.
Those stanzas also show how much the sound matters. Each one runs ABABCCCD. Three rhymes pile up in a row, and they are mostly feminine rhymes, ending on an unstressed syllable: "undo them / through them / glue them," then "forgetting / fretting / petting." The lines are short, with a light, tripping beat. The effect is almost nursery-rhyme playful, and the jingle suits the carefree, unburdened creatures it describes. The final line of each stanza has its own rhyme that reaches across the whole poem: "prime," "time," and finally "rhyme."
That last word matters because the third stanza changes everything. It begins with a sigh, "Ah!", and a wish: "would 'twere so with many / A gentle girl and boy!" The wish is crushed at once by a question: "were there ever any / Writhed not at passed joy?" The verb "writhed" is physical and almost violent, and it makes the soft "bubblings" and "sweet forgetting" of the earlier stanzas feel far away. Humans, unlike the tree, "know the change and feel it." Then Keats gives the cruellest condition: "none to heal it, / Nor numbed sense to steal it." The tree and brook are numbed by cold, and the poem treats that numbness as a kindness. Forgetting is a gentle thief that takes the pain away, and people have no such thief.
The same rhyming trick is now turned on grief. "Feel it / heal it / steal it" has the same bouncing triple rhyme as before, but it carries pain instead of play. The tune stays light while the subject has become heavy. The structure of the final sentence matters too. It begins at "To know the change and feel it" and carries on through two more lines before it reaches its verb in the last line: all of that "Was never said in rhyme." The long clause that holds the suffering is the subject of the sentence, and it hangs there until the poem ends. The closing claim is also a little teasing. The poem insists that this experience has never been put into verse, yet it has just done so, in rhyme. It could be a modest admission that grief can't really be captured, or a quiet boast. The poem leaves that open.
What makes it worth reading is how it flips the usual picture of nature and feeling. Winter normally stands for death, and a tree that cannot feel it would seem sad. Here the lack of memory is a blessing, and consciousness, the ability to compare "now" with "then," is the real wound. The phrase "happy, happy" also appears in Keats's "Ode on a Grecian Urn," where the boughs are happy because they are unchanging, so the poem touches an idea that clearly preoccupied him. In under thirty lines, it lets a small, singing form hold a large, sad thought, and it lets the music make the sadness more noticeable.