William Blake admired John Milton more than any other artist, and saw him as his literary and spiritual teacher. He had regular visions in which the poet appeared to him. Blake told one friend that “Milton lov’d me in childhood & shew’d me his face.” To another, he said, "I have seen him as a youth. And as an old man with a long flowing beard. He came lately as an old man.”

Blake was particularly inspired by Milton's epic poem, Paradise Lost (1667), which retells the Biblical story of the Fall of Man through disobedience to God’s will. Blake produced his own set of watercolour illustrations for the poem in 1808. Yet although he loved Paradise Lost, Blake felt that it misrepresented God by presenting him as a distant authoritarian judge. Blake’s own belief was that God and Man were the same. In another poem, The Everlasting Gospel, Blake’s God tells Christ, and through him all human beings, to recognise human divinity:

        “If thou humblest thyself, thou humblest me;
        Thou also dwell’st in Eternity.
        Thou art a Man, God is no more,
        Thy own humanity learn to Adore.”

Blake criticised Milton's prudishness, elevation of reason over the imagination and lack of self-knowledge. He wrote that Milton “was of the Devil’s party without realising it.” So one of his aims in writing Milton was to correct Paradise Lost.

In Blake’s poem, John Milton, trapped in eternity in a weak and sickly state, is sent on a spiritual journey to self-renewal. In Book One, he takes the form of a blazing comet, descending from the heavens and entering Blake’s left foot. The union of the two poets serves both to save Milton, who achieves self-awareness, and to establish Blake as his heir. Blake claims to possess a new prophetic voice, which will help to redeem the world, and rebuild the lost Jerusalem.