In this poem, Blake criticizes society. Tom is a symbol of innocence in the poetry, and lambs are typically used to signify innocence. As the poem progresses, Tom dreams about his pals who are imprisoned and then set free by an angel. This indicates that humanity is capable of changing for the better. Blake also uses language artfully. The phrase "darkest dungeon" appears three times in the poem. Each time, it refers to a different prison. Darkest means black or very deep, and dungeon implies a place of imprisonment. Together, they mean a place where there is no light or freedom from pain. Dacre's father was Sir Hugh Dacre, who was executed in 1554 for treason against Queen Mary I. Sir Hugh had been sheriff of Northumberland and was known for his harsh treatment of rebels during her reign. He may have been responsible for imprisoning Blake's friends. Blake himself was exiled from England and lived in Europe until his death in 1827. This poem is one of William Blake's more political works. It expresses his views on how innocent people suffer due to the actions of others. Blake believed that humanity was capable of changing for the better, but first needed to overcome its own selfish desires.