In William Blake's "The Chimney Sweeper" from "Songs of Experience," several symbols convey deeper meanings and themes. 

Soot: Soot, associated with the chimneys, symbolizes the moral and spiritual pollution from exploiting children. It is not just physical grime but also a metaphor for the corruption of society's values.

Cry of "weep! weep!": The repeated cry of "weep! weep!" is a stark and poignant symbol of the children's suffering. 

Religious Imagery: The poem contains religious imagery and themes, such as references to God, the Church, prayer, and the idea of heaven. These symbols highlight the hypocrisy of society.