The simile comparing Tom’s hair to the wool on “a lamb’s back” (Line 6) invokes the Christian figure of the Lamb of God (or Agnus Dei in Latin). The phrase originates in the exclamation of John the Baptist encountering Jesus Christ: “Behold, the Lamb of God, which taketh away the sin of the world” (John 1:29). It has a prominent place in Roman Catholic liturgy, between the Lord’s prayer and the Communion, where it calls to mind both Christ’s sacrifice on the Cross and the traditional sacrifice of the lamb described in the Old Testament.

In Blake’s poem, Tom’s hair is sacrificed to the demands of the work he performs; it would get in the way as Tom cleans the insides of chimneys, and children with dirty hair would be a nuisance to their guardians. The hair serves as a synecdoche, a figure of speech in which a part represents the whole: The sacrifice of Tom’s hair stands for the sacrifice of Tom, and many poor children like him, to the capitalist hunger for cheap labor and certain individuals’ and institutions’ pretense of helping those whom they exploit. Like elsewhere in Songs of Innocence, Blake sets forth a parallel between the lamb and the child, both representing purity and lack of guile, precious yet vulnerable to predation and exploitation.