The Principle of the Cross
The first book I ever read in Norwegian has greatly impacted my life for the past 25 years or so. It's an unassuming book with a bland cover and set in a monospaced font (which is terrible for long reads). Even though it was a struggle to consume so much of a language in which I was far from fluent, it was worth it. The book? Korsets Prinsipp (The Principle of the Cross) by Swedish pastor Pelle Karlsson.
So what is the Principle of the Cross? In a nutshell: To lose is to win.