As a student of spiritual theology, I am occasionally asked about it. The simple answer is that I teach prayer. But this is the longer answer:
Spiritual theology is that part of theology that, proceeding from the truths of divine revelation and the religious experience of individual persons, defines the nature of the supernatural life, formulates directives for its growth and development, and explains the process by which souls advance from the beginning of the spiritual life to its full perfection. (Jordan Aumann, Spiritual Theology, Westminister: Christian Classics (1987) 22)
Spiritual theology seeks the connection between the articles of the faith, the perfection of the Christian life, and a kind of knowledge called “mystical,” a kind of knowledge arrived at through an ecclesial and personal encounter with the Living God. In doing so, it is not primarily concerned with individual religious experience although considering such experience is not beyond its scope. More properly it considers the spiritual life of the Church: how is Christ communicating his divine life to his mystical body, his bride?
The answer to this question involves mystical knowledge that results from encountering Christ. This kind of knowledge is “mystical” insofar as it involves a union with the mystery of Christ through the holy mysteries unto union with the Holy Trinity. It is a contemplative knowledge that anticipates the ultimate end of the Divine Economy, the perfect unity of creatures with the Holy Trinity in which the fulfillment of all desire is realized – that eternal beatific vision of inexhaustible and exceeding Love. The object of spiritual theology as a science is the encounter of the Holy Trinity in the contemplation of the Church. In this sense, spiritual theology corresponds with what the ancients called theology or mystical theology. Namely, a participated knowing of the ineffable inner life of the Trinity by grace.
Those who attempt to study this kind of knowledge aim at true theological wisdom, a wisdom that ought to inform all the various branches of theology. In itself, this knowledge is beyond the ability of human speech to fully communicate. But the truth bearing statements of our faith, the articles of our faith, bear the truth of this knowledge above all. Theologians and mystics struggle to articulate it. Garrigou-Lagrange observes, “The mystics … explain the hyperbole and antithesis to which they have recourse in order to draw us from our somnolence and to try to make us glimpse the elevation of divine things.” He goes on to conclude, “No one can know the true meaning of the language of the spiritual writers if he is unable to explain it theologically; and, on the other hand, no one can know the sublimity of theology if he is ignorant of its relation to mysticism.” Three Ages of the Spiritual Life, trans. Sr. Timothea Doyle, OP, London: Herder (1948) pp 16 and 20.
After the great scholastics who revived interest in a disciplined pursuit of these questions, one of the earliest pioneers of this study was Rev. Jean Gerson, Chancellor of the University of Paris. He believed that the knowledge which flowed from Christ's presence in the soul or mystical knowledge could not be a direct object of theological research, yet at the same time he acknowledged its importance for the Christian life and attempted to elucidate those parts fo the Christian life he believed could be studied. From the 16th to the 20th centuries, spiritual theology became divided between what was called “ascetical” theology and “mystical” theology. Ascetical theology had more a moral element and concerned the day to day discipline of the Christian life and the ordinary life of grace. Mystical theology tended toward a theology of prayer and contemplation as well as speculative considerations of the mysteries of the faith in relation to extraordinary mystical phenomenon. Twentieth century theologians began to question the wisdom of separating these areas of study. They also became concerned that this kind of theology was not considered ‘academic’ or ‘scholarly’ or in any other sense a serious field of knowledge.
The 20th century pioneers of this field, mostly Thomists, began an apologetic to establish the field as a legitimate science with its own object and appropriate method of research. At the same time, theologians coming from the Ressourcement schools also became aware that this branch of theology should not be separated from other theological efforts, that these other branches needed reference to spiritual theology if they were to remain with the stream of the tradition of the Church. Spiritual theologians, especially those out of the Thomistic and Ressourcement schools, see that research in spiritual theology is vital to the life and mission of the Church because if it is forgotten, the very raison d’etre of the Church is at risk. As one of the pioneers of the twentieth century renewal of this field, Fr. Juan Arintero, explains: “We must examine and consider attentively the hidden and mysterious development of the inner life of the Church. This consideration is fundamental and the most important of all, because this inner life and the exigencies of this vital process are the course of the Church’s development in doctrine and organization.” Mystical Evolution, vol. 1., trans. Jordan Aumann, Tan: Rockford (1978) 1.