At William Blake's death, a number of poems, completed and incomplete, were discovered among his papers. He seems to have been wary of revealing his own spirituality during his lifetime, for instance:
The vision of Christ that you do see
is my vision’s greatest enemy…
Both read the Bible day and night,
but you read black where I read white.
Blake himself was a visionary, that is, he saw visions and sometimes drew them, as in his renowned illustrations of Dante's Divine Comedy. These poems, however, are of a practical nature, sometimes earthy, as in his "Proverbs of Hell": "What is now proved was once only imagined." and such.
One section is titled There Is No Natural Religion; the next: All Religions Are One.
These writings are of a thoughtful person.