Shelley leaves a city and almost at once begins cross-examining himself about whether he is allowed to. Judging by the title and the opening address to "Cambria" (an old name for Wales), the poem is a farewell to London and a greeting to the mountains. But the pleasure of arrival is quickly shadowed by guilt, and the real subject is the conflict between withdrawing into beautiful scenery and staying loyal to the suffering people left behind.
The first stanza treats landscape as a tonic that hardens rather than soothes. The wind is "unfettered", and he feels it "even now methinks", so it is imagined before it is actually felt. It chases "the clouds that roll in wrath behind", which turns London into a storm he has outrun. Its effect is "tightening the soul's laxest nerves to steel", an image of tuning and toughening, not relaxing. Against "Custom's obduracies", the stubborn hardness of social habit, he sets "mountain Liberty." The rhymes reinforce the idea. The recurring B-sound gathers "feel", "steel", "heal" and "steal", so sensation, strength and cure all chime together. Even the daring "steal / One draught from Snowdon's ever sacred spring" suggests that merely imagining the mountain is enough to wipe out the world's corrupting advice, the "unholiest rede".
Then the mood turns. The second stanza is a run of anxious questions: can "Snowdon's Lethe" make a free mind forget "the page of injured penury"? Lethe is the river of forgetfulness in Greek myth, and Shelley's fear is that natural beauty might work like an anaesthetic. The pressure of the questions builds toward a sharp contrast between "millions famish even in Luxury's hall" and a Tyranny that is "high raised" yet "stern lowers on all". The verb "lowers" means to scowl, but it also drags the tyrant's height down into menace.
The third stanza answers with a firm "No, Cambria!" and a curse on any heart "so false to hope and virtue". The key moment is "For me!...", where the trailing dots make him pause before announcing his purpose. He burns to "wield" a weapon, but what he seeks "amid thy rocks to ruin hurled" turns out to be a flag, "Reason's flag", the "symbol of bloodless victory." The picture of wreckage becomes a picture of peaceful victory. The stanza's last line stretches beyond the others into a long closing line, "A meteor-sign of love effulgent o'er the world", so the form itself seems to unfurl.
The poem is built throughout in nine-line stanzas. Each has eight lines of iambic pentameter and a longer final line, rhymed ababbcbcc. That is the Spenserian stanza pattern. Its interlocking rhymes keep forcing the argument to circle back on itself, which suits a speaker who keeps returning to his doubts. The long last line works like a wave breaking at the end of each stanza, a place for summing up or for a surge of feeling.
In the text as given, a row of dots separates the third and fourth stanzas, and the final stanza reads like a changed, quieter voice. It is a prayer for calm: "calm each struggling thought". It asks that "Let me forever be what I have been" and calls himself "the friend of the unfriended poor", a phrase where the repeated root of "friend" and "unfriended" makes loyalty sound like a vow. The ending is not triumphant. Instead he fears that his own anger might "madly stain their righteous cause in gore." The "weapon" he burned for in stanza three is now something to be held back.
This is what makes the poem worth reading. It refuses both easy options, comfortable retreat and righteous violence. Nature is not an escape but a place to temper conviction, and the hardest struggle is with the speaker's own impulses. The poem is hopeful about reason and love as forces for change, yet it ends by admitting how fragile that hope is.