In this poem, Blake is trying to dispel the myth of grandeur and glory associated with London and to show the "real" people of London and how they felt. London was seen and portrayed as a powerful and wonderful city where the wealthy lived and socialised. However, Blake knew that London was really a dirty, depressing and poverty-stricken city filled with slums and the homeless and chronically sick. To reveal the truth, Blake combines description of people and places with the thoughts and emotions of the people. For example, the second stanza says: "In every cry of every Man, In...
also encouraging the church, and the aristocracy to help the common people and to support them instead of pushing them away and disregarding them.

All of these things are not surprising, considering that Blake was born and lived in London in poverty from 1757-1828. He was a republican and was against the monarchy and probably the aristocracy who supported them, and is said to have had his own version of Christianity. Knowing this "frame of reference", it is not surprising that he wrote a poem such as "London", because he was talking about things that he knew and understood.