This book offers a fresh theological perspective on faith by exploring its gnoseological and metaphysical foundations. It recovers the existential aspects of faith by engaging with the thought of Descartes, Hume, Kant, Fichte, Hegel, Heidegger, and the Christian existentialism of Kierkegaard. This study is informed by the dynamic Thomistic lens developed by Cornelio Fabro (1911-1995), one of the most original twentieth-century commentators on Thomas Aquinas and a preeminent specialist on Kierkegaard and the phenomenon of militant modern atheism. In harmony with the guidelines presented by John Paul II in number 67 of Fides et Ratio (1998), the book will be of particular interest to students and professors of fundamental theology. This study will also provide a philosophical foundation for Christians interested in a deeper knowledge of their faith, and a stimulating topic for anyone questioning the openness of the human being to the Absolute.