William Blake 
The Marriage of Heaven and Hell 

The Prophets Isaiah and Ezekiel dined with me, and I asked them how they dared so roundly to assert that God spoke to them, and whether they did not think at the time that they would be misunderstood, and so be the cause of imposition.
Isaiah answered: 'I saw no God, nor heard any, in a finite organical perception: but my senses discovered the infinite in everything; and as I was then persuaded, and remained confirmed, that the voice of honest indignation is the voice of God, I cared not for consequences, but wrote.’
Then I asked: 'Does a firm persuasion that a thing is so, make it so?’
He replied: 'All poets believe that it does, and in ages of imagination this firm persuasion removed mountains; but many are not capable of a firm persuasion of anything…’