By involution, I mean that Kafka's stories, to a greater extent than just about any other writer, forestall the influence of "outside" forces. His worlds do not rely on historical context, and his characters hardly, if ever, propose a new and narrative-changing idea from whole clothe, although the conclusions they draw are often strange, novel, and sudden. Kafka's land surveyor in The Castle is always circling back to the fact that he is a land surveyor as the basis for his behavior, even though he never actually fulfills or comes close to fulfilling his vocational imperative.
I always recommend Reiner Stach's three volume biography of Kafka to people. The author does a great job of looking into the literature as much as he looks into the life.
There's a bit in the aforementioned interview where they mention if one is learning German, a good introductory route is reading Kafka and Heidegger's Being and Time. I've been contemplating whether I should learn German to read my favorite thinkers in their primary written language (and even potentially make a move to Germany, away from the weariness of California), or, rather, become more grounded in the English language.
Little useful is extracted, it's mainly academics grooming each other over their cleverness. I just couldn't bear it any more.