Harnack's epoch-making work was his _Lehrbuch der Dogmengeschichte_, 1886-88, fourth edition, 1910. The book met, almost from the moment of its appearance, with the realisation of the magnitude of that which had been achieved. It rested upon a fresh and independent study of the sources. It departed from the mechanism which had made the old treatises upon the history of doctrine formal and lifeless. Harnack realised to the full how many influences other than theological had had part in the development of doctrine. He recognised the reaction of modes of life and practice, and of external circumstances on the history of thought. His history of doctrine has thus a breadth and human quality never before attained. Philosophy, worship, morals, the development of Church government and of the canon, the common interests and passions of the age and those of the individual participants, are all made tributary to his delineation. Harnack cannot share Baur's view that the triumph of the Logos-Christology at Nicæa and Chalcedon was inevitable. A certain historic naturalness of the movement he would concede, the world on which Christianity entered being what it was. He is aware, however, that many elements other than Christian have entered into the development. He has phrased his apprehension thus. That Hellenisation of Christianity which Gnosticism represented, and against which, in this, its acute form, the Church contended was, after all, the same thing which, by slower process and more unconsciously, befell the Church itself. That pure moral enthusiasm and inspiration which had been the gist of the Christian movement, in its endeavour to appropriate the world, had been appropriated by the world in far greater measure than its adherents knew. It had taken up its mission to change the world. It had dreamed that while changing the world it had itself remained unchanged. The world was changed, the world of life, of feeling and of thought. But Christianity was also changed. It had conquered the world. It had no perception of the fact that it illustrated the old law that the conquered give laws to the conquerors. It had fused the ancient culture with the flame of its inspiration. It did not appreciate the degree in which the elements of that ancient culture now coloured its far-shining flame. It had been a maker of history. Meantime it had been unmade and remade by its own history. It confidently carried back its canon, dogma, organisation, to Christ and the apostles. It did not realise that the very fact that it could find these things natural and declare them ancient, proved with conclusiveness that it had itself departed from the standard of Christ and the apostles. It esteemed that these were its defences against the world. It little dreamed that they were, by their very existence, the evidence of the fact that the Church had not defended itself against the world. Its dogma was the Hellenisation of its thought.