In his Latin theological textbook, Bernard Lonergan proposed a way of correlating the four trinitarian relations (paternity, filiation, active spiration and passive spiration) with four distinct participations in the divine nature vis. the Incarnation, the beatific vision, sanctifying grace and the habit of charity. This book uncovers the genetic origins of this hypothesis in Augustine and Aquinas, its significance in terms of the grace-nature debate, and the insights it provides to key Christian doctrines such as Christology, ecclesiology, the nature of holiness, and the beatific vision. The author engages with contemporary theological literature to demonstrate the explanatory power of Lonergan's construct in relation to competing proposals. Vatican I taught that the role of systematic theology is to understand divine mysteries through analogy and through the nexus between these mysteries. This work argues that Lonergan's hypothesis perfectly fulfils the second of these tasks and thus provides a needed unification of the diverse topics that confront systematic theologians. Each individual chapter has appeared in leading theological journals: Theological Studies, Irish Theological Quarterly and Louvain Studies. The chapters are ordered here not in terms of publication date, but in such a way as to guide the reader through a more synthetic grasp of the issues involved.