The second stanza actually contains one of the most famous lines of this poem and of Blake's poetry as a whole. Let us remember that the first stanza begins as the speaker is wandering through London and considering the "Marks of weakness, marks of woe" that he sees in the faces of those that he passes. The second stanza moves on to focus exclusively on the people that he sees as he ventures on and the kind of sadness and deep despair that they experience:
In every cry of every man,
In every infant's cry of fear,
In every voice, in every ban,
The mind-forged manacles I hear:
The speaker sees in all the misery that surrounds him "mind-forged manacles" that are binding the people that he meets to the poverty and despair that characterises their life. This phrase of "mind-forged manacles" is incredibly significant and suggests that actually so much of the reason behind poverty is that we are enslaved to institutions and bodies that sustain and create poverty and that this is unnecessary.