Martin Buber's 1923 meditation distinguishes between two modes of relation: I-It, in which we treat the world as objects to be used, and I-Thou, in which we encounter another presence as a whole being. The Thou can be a person, nature, or God. The prose is aphoristic, almost mystical, and the influence on twentieth-century theology and philosophy has been immense. Buber wrote in German, but the ideas transcend language. The book is brief, difficult, and capable of changing how you experience every encounter.