Anyone familiar with the gargantuan theological output of the German Jesuit theologian Karl Rahner (1904–1984) can hardly miss the irony that for someone who is universally hailed as the most influential contributor to the renaissance of trinitarian theology in the twentieth century, at least in the Catholic Church, and who vigorously insists that the Trinity be the center of theology and Christian life, the bulk of his explicit writings on the Trinity is minuscule. His synthetic magnum opus Grundkurs des Glauben (Foundations of Christian Faith) contains barely four pages on the Trinity, entitled “Towards an Understanding of the Doctrine of the Trinity.” Apart from a handful of pieces in his Schriften zur Theologie (Theological Investigations) and two entries in the encyclopedia Sacramentum mundi, Rahner's longest writing on the Trinity is a booklet-length contribution to a handbook of theology.

Why, then, in spite of the paucity of his writings on the Trinity, is Rahner celebrated as the initiator of the rediscovery of the Trinity in Catholic theology? Does this paucity reflect a lack of consistency between Rahner's theory and praxis? Or could it be argued that it is precisely because the Trinity so thoroughly informs the structure and contents of Foundations of Christian Faith that a lengthy treatment of it is unnecessary? What is so significant about his trinitarian theology, and in which ways has it renewed the Christian theology of the Trinity? To answer these questions would require, first, situating Rahner's trinitarian theology in the context of the Catholic neo-scholastic or manualistic theology which was the staple fare in Catholic seminaries until the 1960s and, second, examining in detail, albeit within a very limited space, its major tenets.