The theme of lost innocence is particularly evident in the contrast between the poem's two parts. In Songs of Innocence, the young chimney sweeper maintains his innocence despite his dire circumstances. He describes a dream in which an angel frees him and other sweepers. This portrayal of innocence emphasizes the purity of childhood and the hope that it can be preserved even in the face of hardships. 

The poem ends optimistically: "So if all do their duty, they need not fear harm." This is a naive and innocent understanding of the world: in reality, the boys do their duty but are still put to work in deadly environments. 

In contrast to this innocence and naivety, Songs of Experience presents a harsher reality where the chimney sweeper has lost his innocence and has become bitter and disillusioned. The poem critiques the exploitation of children and dismisses the promises of an afterlife, reflecting the harsh experiences the children have endured. While religion offered some hope to Tom Dacre and the other chimney sweepers in Songs of Innocence, the chimney sweeper in the later poem recognizes that the Church has done nothing but "make up a heaven of [the sweepers'] misery."

These two contrasting perspectives on innocence and experience illustrate how societal conditions can corrupt the purity of childhood, and they condemn the moral and social failings of the time.

With this poem, Blake offers a scathing rebuke of institutionalized religion. In Songs of Experience, in particular, the poet questions the Church's role in perpetuating the suffering of children and condemns its empty promises of salvation.

This theme reflects the Romantic-era poets' skepticism of organized religion and its unquestioned moral authority. The poems suggest that religion, in its institutionalized form, often fails to protect and care for the vulnerable people in society. Instead, it perpetuates social injustices by allowing people to dismiss the evils around them. It is significant that instead of caring for the "little black thing among the snow" and helping the chimney sweepers, the parents go to church to "praise God and his Priest and King." 

Blake appears to dismiss the Church's teachings about a heavenly afterlife. Tom and the other sweepers only reach paradise in their dreams. When they wake up before dawn each morning, they still must get to work in their harsh conditions. The promise of a reward and release from this daily toil only in death is a cruel joke to Blake.

Blake's poems serve as a reminder that religion, when it becomes intertwined with societal power structures and fails to advocate for justice and compassion, can lead to more suffering, contribute to the loss of innocence among the vulnerable, and ease the remorse of the callous and complicit.

A significant theme in Blake's poems is the dehumanizing impact of industrialization on society, especially on the lives of children forced into labor. The chimney sweepers in Blake's poems are symbolic of the larger issue of child labor during the Industrial Revolution.

When my mother died I was very young,
And my father sold me while yet my tongue
Could scarcely cry "'weep! 'weep! 'weep! 'weep!"
So your chimneys I sweep & in soot I sleep.

With this opening stanza, Blake highlights the heart-wrenching reality of young children being sold into labor due to economic pressures. It is meant to be a sharp critique of the societal norms that allowed such exploitation to occur and a reminder that unchecked economic progress is not free from negative consequences.

Today, most countries have laws prohibiting dangerous and exploitative child labor practices. However, discussions concerning child labor and workers' rights remain ongoing. Blake's poems serve as a reminder of the human cost of rapid industrial development and the need to protect workers of all ages and backgrounds from exploitation.