From a Van Gogh letter

Vincent van Gogh to his mother Anna Cornelia, c. June 12, 1890:

I was struck by what you say in your letter about having been to Nuenen. You saw everything again, “with gratitude that once it was yours” — and are now able to leave it to others with an easy mind. As through a glass, darkly — so it has remained; life, the why or wherefore of parting, passing away, the permanence of turmoil — one grasps no more of it than that.

For me, life may well continue in solitude. I have never perceived those to whom I have been most attached other than as through a glass, darkly.

The Letters of Vincent van Gogh , ed. Ronald de Leeuw, trans. Arnold Pomerans (New York: Penguin, 1997).

“I have never perceived those to whom I have been most attached other than as through a glass, darkly”: one can find similar statements in Willa Cather’s fiction. From The Song of the Lark (1915):

He looked down wonderingly at his old friend and patient. After all, one never knew people to the core.

And from The Professor’s House (1925):

The heart of another is a dark forest, always, no matter how close it has been to one’s own.

These passages are a matter of what is sometimes called free indirect discourse: they represent a character’s thinking. But they’re very Cather.

Our household is full of Van Gogh and Cather. We went up to Art Institute of Chicago yesterday to see Van Gogh’s Bedrooms one more time. We stood communing with Jules Adolphe Breton’s The Song of the Lark , just like Thea Kronborg. And then we wandered the ten floors of the Fine Arts Building, which plays a part in Lucy Gayheart (1935).

Also from Van Gogh’s letters
“Admire as much as you can”
“It was a bright autumn day and a beautiful walk”
“Lately, during the dark days before Christmas”
“So you must picture me sitting at my attic window”
“At the moment, I can see a splendid effect”
“The ride into the village was beautiful”
“A colourist the like of which has never yet been seen”