In Blake's poem from Songs of Innocence, Tom Dacre is a young boy who was most likely sold into the difficult business of sweeping chimneys. Orphans or illegitimate children were often given to the Church to raise, who in turn would give them to chimney sweepers so that they could earn their keep. As a young body, they fit more easily into chimneys, though the work was terrible and the hazards quite apparent. Many chimney sweepers developed emphysema from inhaling the toxins in the chimneys. By displacing comfort into an afterlife, adults—including those charged with raising them—are able to ignore the very real human needs denied these boys.
The poem's speaker is, like Tom Dacre, one such boy. In this poem, he has yet to recognize the cruelty that has forced him and others, like Tom, into this type of work. The last line, "So if all do their duty, they need not fear harm," is an innocent echo of the language such boys hear from adults and most likely their church guardians who elide spiritual and physical labor. The poem works through irony, as the reader must close the gap in the irony between what the speaker says and what the real world situation implies.
Tom is like the lamb in that he, too, is innocent. His curly hair offers a physical similarity to the animal, and having his hair shorn links the two in that both become commodities in a world more attuned to money than morals governing the care of helpless creatures. Tom is seen as a creature to be used rather than nurtured. His sweet innocence, like a lamb's, is sacrificed for other people's material comforts. The link between Christ as the Lamb of God is also worth considering, given the language in this poem. Like Tom, Christ also seems to be used for human profit.