Why did William Blake write "Auguries of Innocence"?

William Blake wrote "The Auguries of Innocence," a poem that was not published until years after his death, to affirm the great importance of small, seemingly insignificant details of life. It is a cry of anger against the petty cruelties of human society. Some have called it a summary of the philosophy he expresses in his Songs of Innocence and Experience.
Blake refused to belong to any church and rejected organized religion—he viewed it as filled with hypocrisy. To him, the church too often overlooked or rationalized suffering and pain, especially the suffering of innocent creatures without power, such as children and animals.
In the poem, Blake describes some of the suffering that many would brush off as unimportant, arguing that this pain does, in fact, matter greatly. For example, he writes that a caged robin enrages heaven, and a starving dog "predicts the ruin of the State."
All of life is interconnected, Blake argues. He states near the end of the poem that unless we see life through the eyes of those who are suffering ("Born in an Night to perish in a Night"), we "Believe a Lie."