This book rethinks the problems of subjectivity through the neglected tradition of French Spiritualism, arguing that modern philosophy's deepest impasses--regarding subjectivity, mediation, relationality, and transcendence--arise from a failure to account for the dynamic and relational character of being. Drawing on the resources within French Spiritualism, the book develops an original conception of ontology in which subjects become themselves, not through domination or control, but through receptive action and mediation. Subjectivity emerges not as sovereign self-possession, nor as postmodern dissolution, but as a dynamic and erotic navigation poised between activity and passivity. The study ranges across metaphysics, philosophy, and theology, showing how the insights of French Spiritualism illuminate contemporary debates. In its constructive climax, the book advances a trinitarian version of existentialism based on an erotic ontology of the subject, suggesting that the deepest logic of reality is neither static substance nor pure flux, but relational and generative love. Historically rigorous and philosophically inventive, this book will interest scholars in continental philosophy, theology, religious studies, and intellectual history, as well as readers seeking a richer metaphysical vision capable of reuniting thought, life, and transcendence.