The figure of the prophet is rooted in Old Testament Literature. The priests were in charge of the religious activities of the Jews. They developed a religion based on law. The ten commandments of Moses multiplied until there were laws and rules for every facet of Jewish life. Following the law was supposed to please Jehovah and induce him to protect the Israelites. But the law was broken in letter and in spirit, and the nation of Israel endured many calamities which was often interpreted as punishment from Jehovah for sinfulness. Prophets arose outside of the established religious organization to lay before the people their failures and the predicted consequences. The prophets spoke as instruments of God, attempting to lead the people into more a just, merciful, and equitable society. The Old Testament prophets usually used threats as well as promises in trying to induce the Israelites to be obedient to God as they understood him.
Blake, with his sensitivity to injustice, and his vision of the elevated role man should play in God's world, felt affinity for the role of prophet. He knew how the world could be, should be, and would be if man would recognize and accept the role that God offers him.
God had endowed William with outstanding gifts. He had an unusual ability to see beyond the superficial appearances around him. He had an intellect that could absorb vast amounts of information and analyze and organize it. He had communication skills as a verbal and visual artist. Recognizing these talents as gifts from God, he wanted to use them in His service.
So it seems predictable that Blake should assume the role of prophet, and attempt to lead the people into a better understanding what had gone wrong with the plans God had for mankind, and how man might get back on the right track. The right track to him was not obedience to the law as it was for the prophets of old; the right track was the New Testament innovation of being led by the Holy Spirit.
Blake created the character Los as the Eternal Prophet, and allowed him to enact many of the prophetic roles Blake played himself. Like the prophet Ezekiel, Blake and Los used demonstrations, not words alone to project their message.
"I rest not from my great task!
To open the Eternal Worlds, to open the immortal Eyes
Of Man inwards into the Worlds of Thought: into Eternity
Ever expanding in the Bosom of God. the Human Imagination"
"Giving a body to Falshood that it may be cast off for ever."
"The blow of his Hammer is Justice. the swing of his Hammer:
The force of Los's Hammer is eternal Forgiveness"
"Because he kept the Divine Vision in time of trouble"
The Voice of One Crying in the Wilderness