From Modern Painters, vol. 3 (Works, V, 333)
…the more I think of it I find this conclusion more impressed upon me, – that the greatest thing a human soul ever does in this world is to see something, and tell what it saw in a plain way. Hundreds of people can talk for one who can think, but thousands can think for one who can see. To see clearly is poetry, prophecy, and religion, – all in one.