The Vocation of Man (Hackett Classics)
Johann Gottlieb Fichte
A standard text in the world of undergraduate classes in European philosophy*, Fichte is a bridge of sorts between Kant and Hegel. If memory serves, we read this book not for its thoughts on the nature of faith, but for its use of the dialectic. My memory of this is vague, but the class I read it for was one of the most difficult of my undergraduate curriculum. This and the other troublesome Germans we read had a lot to do with that.
Not a major work, for pleasure reading or self-improvement, I think you’d be better off with some of the other Germans.
*by professors unconcerned with Fichte’s reputation for anti-Semitism, something I didn’t know about when I read this.