Which major work presented Gabriel Marcel’s ideas most systematically?

The most systematic presentation of Gabriel Marcel’s philosophical ideas is found in his two-volume work titled The Mystery of Being (originally published in French as Mystère de l’être in 1951). This work was based on the Gifford Lectures he delivered at the University of Aberdeen between 1949 and 1950.1

While Marcel is known for a philosophical style that often eschewed traditional systematic approaches in favor of a phenomenological, diary-like, or dramatic method of "discursive probing," The Mystery of Being serves as the primary exception where he organized his thoughts more formally.1