The Destruction of Innocence
Throughout both Songs of Innocence and Songs of Experience, Blake repeatedly addresses the destruction of childlike innocence, and in many cases of children's lives, by a society designed to use people for its own selfish ends. Blake romanticizes the children of his poems, only to place them in situations common to his day, in which they find their simple faith in parents or God challenged by harsh conditions. Songs of Experience is an attempt to denounce the cruel society that harms the human soul in such terrible ways, but it also calls the reader back to innocence, through Imagination, in an effort to redeem a fallen world.
Redemption
Throughout his works, Blake frequently refers to the redemptive work of Jesus Christ. While he alludes to the atoning act of Christ Crucified, more often Blake focuses on the Incarnation, the taking on of human form by the divine Creator, as the source of redemption for both human beings and nature. He emphasizes that Christ "became a little child" just as men and women need to return to a state of childlike grace in order to restore the innocence lost to the social machinery of a cruel world.
Religious Hypocrisy
In such poems as "Holy Thursday" and "The Little Vagabond," Blake critiques the religious leaders of his day for their abuse of spiritual authority. The men who should be shepherds to their flocks are in fact reinforcing a political and economic system that turns children into short-lived chimney sweepers and that represses love and creative expression in adults. Blake has no patience with clergy who would assuage their own or their earthly patrons' guilt by parading poor children through a church on Ascension Day, as in "Holy Thursday" from both sections, and he reserves most of his sharpest verse for these men.
Imagination over Reason
Blake is a strong proponent of the value of human creativity, or Imagination, over materialistic rationalism, or Reason. As a poet and artist, Blake sees the power of art in its various forms to raise the human spirit above its earth-bound mire. He also sees the soul-killing materialism of his day, which uses rational thought as an excuse to perpetuate crimes against the innocent via societal and religious norms. Songs of Experience in particular decries Reason's hold over Imagination, and it uses several ironic poems to undermine the alleged superiority of rationalism.
Blake was not opposed to intelligent inquiry, however. In "A Little Boy Lost" from Songs of Experience, Blake admires the boy's inquiries into the nature of God and his own Thought, even as he sharply criticizes the religious leaders of his day for demanding mindless obedience to dogma.
Nature as the Purest State of Man
Like many of his contemporary Romantic poets, Blake sees in the natural world an idyllic universe that can influence human beings in a positive manner. Many of his poems, such as "Spring," celebrate the beauty and fecundity of nature, while others, such as "London," deride the sterile mechanism of urban society. Blake's characters are happiest when they are surrounded by natural beauty and following their natural instincts; they are most oppressed when they are trapped in social or religious institutions or are subject to the horrors of urban living.
The Flaws of Earthly Parents
One recurring motif in both Songs of Innocence and Songs of Experience is the failure of human parents to properly nurture their children. The "Little Boy Lost" is abandoned by his earthly father, yet rescued by his Heavenly Father. The parents of "The Little Vagabond" weep in vain as their son is burned alive for heresy. Both mother and father seem frustrated by their child's temperament in "Infant Sorrow." This recurring motif allows Blake to emphasize the frailty of human communities, in which the roles of mother and father are defined by society rather than by natural instincts, and to emphasize the supremacy of Nature and of divine care in the form of God the Father.
Social Reform
While much of Blake's poetry focuses on leaving behind the material world in favor of a more perfect spiritual nature, his poetry nonetheless offers realistic and socially conscious critiques of existing situations. Both of his "Chimney Sweeper" poems highlight the abuse of children by parents and employers as they are forced into hazardous, and potentially fatal, situations for the sake of earning money. Both "Holy Thursday" poems decry the overt display of the poor as a spectacle of absolution for the wealthy and affluent. "The Human Abstract" points out that our virtues are predicated on the existence of human suffering. Although Blake is certainly more spiritually than practically minded, the seeds of social reform can be seen in the philosophy underlying his verses: innocence is a state of man that must be preserved, not destroyed, and the social systems that seek to destroy innocence must be changed or eliminated.