This is from an article by Sixten Ringbom, Art in the ‘epoch of the great spiritual’, published in 1966.
In the article, which is quite interesting, we also learn that Paul Klee thought anthroposophy was ‘either false or a piece of self-deception’. (Though, Ringbom points out, Klee’s own ideas were hardly more rational.)
I came across it when meandering my way through the internet, reading all kinds of things about art inspired by occultism and esotericism, because, well, I’m still obsessed with Hilma af Klint and one thing led to another. (Perhaps someone will enjoy this article! I did.) And because I recently read Kandinsky’s On the spiritual in art. Fascinating indeed. And I realize that I must read more by Steiner on art. Ringbom mentions, among other texts, this piece.
Ringbom’s article is available for free, but you have to register to read it. You’ll find it here.