Søren Kierkegaard's 'The Sickness Unto Death,' published under the pseudonym Anti-Climacus, is a profound and influential work of Christian existentialism. It offers a penetrating analysis of despair, which Kierkegaard defines not merely as an emotion but as a fundamental spiritual illness—a 'sickness of the spirit, of the self.' The book meticulously dissects various forms of despair, including despair at not willing to be oneself, despair at willing to be oneself, and despair in defiance. Kierkegaard posits that true despair arises from a separation from God, and he presents faith as the ultimate antidote. This seminal text compels readers to confront their spiritual condition and the intricate relationship between human existence and the divine.