The article considers the reflection of the basic laws of the mystery of the XIV–XVI centuries in the musical and theatrical works of the French "synthetic theater" of the twentieth century. These are "The Martyrdom of Saint Sebastian" by G. d'Annunzio — C. Debussy (1911) and "The Good News of Mary" by P. Claudel (1912-1948). The purpose of the work is to establish the peculiarities of the operation of the principles of semantics and composition of the genre, revived at the end of the XIX century and further developed in the French musical theater. In interdisciplinary, hermeneutical and art criticism approaches to achieving this goal, we distinguish a comparative method that allows us to draw conclusions about the identity and difference of the elements of these works, as well as about the genre "codes" of mystery dramas that enter into dialogue over a significant (about 300 years) time interval. We are talking about a dialogue within the history of Western European theater. In favor of the scientific novelty and significance of the work, we present theses on the integration of the spiritual dimension into the space of the mystery drama of the twentieth century, as well as on the relevance of the spiritual messages of the French composers of the twentieth century, who created mystery dramas in line with the Christian tradition. Conclusions are drawn: About the functions of liturgical choirs in Latin in French mystery dramas of the twentieth century, revealing the spiritual meaning of the works considered in this article. On the interaction of the sacred and profane as the leading genre feature of the mystery drama of the XIV–XVI centuries and the twentieth century. About the preservation of the spatial vector "earth — sky" by the French mystery drama of the twentieth century. On the connection of the French mystery drama of the twentieth century with the spiritual problems of modernity. About the search by the French mystery drama of the twentieth century for the possibility of overcoming the discrepancies between the world, God and man. About the inclusion of the French mystery drama of the twentieth century in the general cultural context.