Shelley builds the poem on a riddle-like comparison. Chameleons, he says, "feed on light and air," while poets live on "love and fame." The three stanzas then work as three moves in one argument: a puzzle, an explanation and a warning.
The first stanza asks what would happen if poets had their food as easily as chameleons have theirs. Would they "ever change their hue / As the light chameleons do, / Suiting it to every ray / Twenty times a day?" The question carries its own answer. Poets shift and adapt because they are hungry, not because they are fickle. The tone is light and teasing, and the stanza ends on a tiny line, "Twenty times a day?", that sounds almost like a shrug.
The second stanza gives the reason. Poets are on "this cold earth" as chameleons would be if they were "hidden from their early birth / in a cave beneath the sea." The picture is oddly sad: a creature whose whole talent is responding to light, born where there is none. The grammar then turns neatly on itself: "Where light is, chameleons change: / Where love is not, poets do." The sentences are parallel, but the meanings are opposites. Chameleons change toward something, while poets change because something is missing. "Fame is love disguised" extends the idea, since fame becomes a costume love wears, a second-best that poets chase when the real thing is scarce. Because "few / Find either," poets "range." The word means both to wander restlessly and to cover a spread of colours, so the idea and the metaphor are packed into one verb.
The form is tightly controlled. Each stanza has nine lines and the same rhyme pattern, ABABCDDCC. The lines are short, mostly four beats of seven or eight syllables, with a falling rhythm that puts weight on nearly every word of "Poets' food is love and fame." Each stanza ends on a clipped line of four or five syllables that snaps shut like a trap: "Twenty times a day?", "That poets range.", "Oh, refuse the boon!" Those last lines sit inside rhyming triplets (change, strange, range; soon, moon, boon), so the ending of each stanza gathers momentum, then stops short.
In the third stanza the title finally makes sense, because an exhortation is an urgent appeal. The teasing disappears with "Yet dare not stain." The verb picks up "hue" from earlier. A chameleon's colour is light and temporary, but a stain stays. Wealth and power would fix the poet in the wrong colour for good. The verb "devour" also sounds greedy and coarse next to the airy "beams and wind," and the "brother lizards" are a small, cutting joke. A chameleon that eats like them would "grow as earthly" as they are, just another ordinary reptile.
The poem's imagery has been moving up and down all along. Down are the "cold earth," the "cave beneath the sea" and the "earthly" lizards. Up are the "sunnier star," the "heavenly mind" and the "Spirits from beyond the moon." By the last lines poets have gone from needy creatures to near-divine beings, and "boon" carries the final irony. A boon is a favour or gift, so wealth and power are imagined as presents offered to the poet. The poem asks him to turn them down because they would bring him back to earth.
What makes the poem worth reading is that it does not pretend this refusal is easy. The first two stanzas take the poet's hunger seriously. Love and fame are real needs, and their absence really does unsettle him. The warning in the third stanza therefore lands harder, because the temptation has been made believable. The poem praises the poet's purity while admitting his vulnerability, and it holds one metaphor steady through all three stanzas. A single odd animal ends up explaining how it feels to be starved, changeable, idealistic and tempted.