Meaning

Hi friends,
I want to know what's the meaning of "burn your eyes clean", "burn clean" in the following text? This text is extracted of o'connor's story (the vilolent bear it away).

“The old man, who said he was a prophet, had raised the boy to expect the Lord's call himself and to be prepared for the day he would hear it. He had schooled him in the evils that befall prophets; in those that come from the world, which are trifling, and those that come from the Lord and burn the prophet clean; for he himself had been burned clean and burned clean again. He had learned by fire.”

“His feeling of oppression was caused now by the certain knowledge that there was no way to get rid of him. He would be with them until he had either accomplished what he came for, or until he was cured. The words the old man had scrawled on the back of the journal rose before him: THE PROPHET I RAISE UP OUT OF THIS BOY WILL BURN YOUR EYES CLEAN.”

Thanks alot