Blake's speaker doesn't so much describe London as listen to it. He wanders through the streets, and what he takes in is a city where everyone seems branded by suffering. The poem's central idea is that this misery is more than poverty or bad luck. It is a system of control, and its most powerful chains are the ones people cannot see.
The word "chartered" comes twice in the opening two lines, attached first to the streets and then to the Thames. A charter is a document that grants rights or licenses, so it should suggest freedom. Here it suggests ownership and boundaries. Even a river, which we think of as running free, has been mapped and claimed. The speaker's own movement is "wandering," but nothing around him is open. The faces he meets carry a "mark," a word that hints at stains, brands and labels all at once. The repeated "marks of weakness, marks of woe" makes the sentence itself feel stamped over and over.
In the second stanza the poem shifts from sight to sound, and "every" takes over. It appears five times in four lines, as if no voice in the city escapes. The cries of men and of frightened infants blur together, and even "ban" works two ways, as a prohibition or as a curse. Then comes the poem's most famous phrase, "mind-forged manacles." A forge is a blacksmith's workshop, so these chains are made deliberately, and the poem leaves open who the smith is. They may be made by the people themselves, who have come to accept their limits, or by those who shape what ordinary people are able to think. Either way, the speaker can "hear" them, and the oppression has become audible.
The form supports this. The rhymes are plain and tightly paired (street/meet, flow/woe), and the opening lines move in a steady beat like footsteps on pavement. The rhythm tightens in the third stanza, where the lines shorten and begin on heavy stresses ("How the chimney-sweeper's cry"). The effect is less like a stroll than like blows. The colon at the end of stanza two pushes us straight into the examples that follow, so the poem has no room to pause.
Those examples turn on a trick of the senses. The chimney-sweeper's cry "appalls" the "blackening" churches. The verb contains the word "pall," the cloth laid over a coffin, and the churches are already darkened with soot. The judgment seems to be that the church tolerates the suffering it is supposed to relieve. Next, the soldier's sigh, a tiny, exhausted sound, "runs in blood down palace-walls." A noise becomes a liquid, and the stain lands on the home of the powerful. The poem never argues this point. It simply makes the image run.
The last stanza begins with "But most," as if the worst has been saved for midnight. The "youthful harlot's curse" blasts a newborn's tear and "blights with plagues the marriage-hearse." That final compound is the poem's harshest. A marriage carriage and a funeral carriage fuse into one, so that love, birth and death are all soiled in the same breath. "Plagues" suggests disease, and the imagery implies that the harm spreads from the margins of the city into its most respectable institutions. The speaker does not scold the young woman. Her curse sits in the same chain of cries as the infant's and the sweep's, which makes her another victim of the system.
The poem ends without any hope or consoling turn. Blake was a poet and engraver who spent most of his life in London, and the poem has the compression of an engraver's work, with every word cut deep. It matters because it changes how we think about oppression. It asks us to look at the actual people in the street, and then to ask what has taught them to accept the chains.