Gilbert Highet read Eugen Herrigel's book, Zen in the Art of Archery, a few years before writing an essay, "The Mystery of Zen," and he uses the eventual impact of that book on him to look at how thought evolves and how we learn about things in a Zen-like way. He spends a lot of the essay talking about what the book is about and also about what else he has learned since then about Zen in general. His own thoughts take up relatively little space in the essay, but they are at the heart of what he is considering.
In the first paragraph, for instance, he discusses the way he has come to learn about things without consciously trying to. This is a very Zen concept, and the fact that Highet can't explain how it happens but has recognized it "a hundred times" provides a great example that the Zen masters are onto something important.
He says that he read the book a few years earlier and found it alien (paragraph 2) but apparently filed it away mentally. He then spends a good amount of time (paragraphs 3-11) detailing how the book came to be and what it covers, concluding, "Zen cannot be analyzed from without; it must be lived" (paragraph 12).
However, because he is still focused on trying to understand Zen, he spends more time writing about Zen and meditation. He has devoted some study to the subject in the years since reading the book (he hints at it in paragraph 3, but he doesn't cite most of his references). The whole essay becomes Highet's interpretation of something that he admits can't really be interpreted or thought about in the way that most philosophies can be studied. By its very nature, Zen is a way of understanding without thinking, and, although Highet tries to think about it anyway, he only succeeds in suggesting the mystery that his title talks about. At least he has the insight to put himself among "the unilluminated" (final paragraph), because the book and all of Highet's research makes it clear that Zen ...