The most systematic work Martin Luther ever created was his De servo arbitrio / The Bondage of the Will (1525), his powerful polemic against the leading Humanist of his day, Erasmus, who had criticized Luther in his De libero arbitrio diatribe sive collatio / The Freedom of the Will (1524). Luther’s The Bondage of the Will is regarded as a work representing the organic unity of his entire theological thought; it can be seen as his theology in a condensed form. In spite of the immense significance of Luther's magnum opus, its theological structure and content have so far not yet been satisfactorily revealed.

Much research has been conducted on certain detailed aspects of this work of Luther’s, such as the problems of the free will, determinism, and predestination. The basic weakness of those analyses is that the details of The Bondage of the Will can be correctly understood only on the basis of a comprehension of the basic systematic theological idea of his work. The very kernel of Luther’s own thought and the deepest intentions of his theology in this work are best comprehended by analyzing the inner structure and cohesion of his own thinking and by seeing how his argumentation developed in his dispute with Erasmus.

The task of this study is to expose the fundamental systematic theological idea and structure in Luther's The Bondage of the Will. The method employed in the present study is a comprehensive systematic analysis of Luther’s thought in his work. Attention will be paid to the conceptualization of issues by Luther, to his main propositions and the arguments he uses to support his claims, and to the structural principles and the core body of his thinking system. The debate between Luther and Erasmus contained genuine paradigmatic differences in their understanding of the Christian faith, but also some misunderstandings, even intentional misinterpretations. The present study aims at clarifying these conceptual confusions and at exploring the possibility of some degree of reconciliation between the conflicting views.

My hypothesis is that Luther’s own specific and comprehensive understanding of the Trinitarian theology of grace, with special emphasis on Pneumatology, alongside the more obvious Christology, strongly linked with the theology of creation, is the fundamental thought structure of his magnum opus. This enables him to get rid of the common Late Medieval teaching of the free choice of the human being, represented by Erasmus. Above all, Luther is a theologian of grace, sola gratia. The Bondage of the Will, the most Pneumatological treatise he ever wrote, offers a radical and comprehensive Trinitarian theology of grace.

Luther understands the human being as an “ecstatic” creature who receives his/her existence and the quality of his/her existence from extra se. Luther argues for this paradigm in terms of the theology of creation, Christology, Pneumatology, and soteriology. As such, the human being was created a creature which is destined for union with his/her Creator in the Holy Spirit who is the actual presence of the Creator in his creature, God sharing his life with the human being. After losing this original state of union, the human being became a battlefield of the opposing transcendental powers, Satan and sin on the one side, and God and his grace, on the other side. The human is free in “things below oneself,” in matters that belong to daily human life, but he/she is not free in “things above oneself,” in matters that transcend the human being. Luther sees sin as human infirmity, inability to get rid of unbelief and pride which destroyed the human’s union with God. The human being cannot change his/her evil orientation but must continue such as he/she is: this is Luther’s concept of “the necessity of immutability”; he applies this philosophical concept to soteriological usage. The human being is in a desperate situation in regard to his/her capacities of contributing to his/her own salvation; here Luther follows his logic of theologia crucis.

Both in terms of creation and salvation, the human being is meant to be in a communion of life with the Triune God. Luther develops a strong soteriology, understood in terms of an intimate union between the Triune God and the human being. This union is not primarily a cognitive-rational and morally responsible relation, as Erasmus was inclined to think, but a union of being with Christ in the Holy Spirit, koinonia/unio cum Christo in Spiritu sancto. The quality of a human being’s life in this world and his/her eternal beatitude depends on whether his/her person is or is not in union with the Holy Trinity. In his Trinitarian theology of grace, Pneumatology, arguably neglected in Medieval times, is powerfully revived. Luther’s conception of divine grace, with some peculiarities of his own, recalls Augustine’s doctrine of grace, differing from the soteriological views of Scholasticism and Nominalism.

The present study culminates in a systematic presentation of the three dimensions of Luther’s Trinitarian doctrine of grace: First, contrition, conversion, and faith are effected by God’s Spirit, sola fide is a thoroughly Pneumatological concept – a fact not sufficiently emphasized in research. Second, Luther sees the union with Christ simultaneously as a Christological and as a Pneumatological reality - a view not underscored in research. Third, sanctification means growth in love by way of being increasingly controlled by the Holy Spirit, who is the essence of divine love. This three-dimensional conception of grace can be supported by other works of Luther’s mature theology.

There are strong points of contact with Johannine, Pauline, Augustinian, and Greek Patristic theology here; a more detailed analysis of these connections, however, is not in the scope of the study at hand. The results of the study intensify the ecumenical potential of Luther’s doctrine of grace. Moreover, these results contribute an amendment to the Finnish school of Luther interpretation where the Pneumatological dimension is underemphasized in the first and the second dimensions of Luther’s doctrine of grace. Finally, the possibility of some degree of reconciliation between the views of Erasmus and Luther will be considered.