In the study of the doctrinal development nothing is so important as the exegesis of the New Testament statements about the Cross; and this has been done in a masterly way by Dr. Dale in his work on the Atonement. What may be called the Philosophy of the Cross (to borrow a happy phrase of McCheyne Edgar's) came late. It is usually reckoned to have commenced with Anselm; and since the Reformation every great theologian has added his contribution. Yet the work is by no means completed. Indeed, at the present day there is no greater desideratum in theology than a philosophy of the Cross which would thoroughly satisfy the religious mind. Shallow theories abound; but the Church of Christ will never be able to rest in any theory which does not do justice, on the one hand, to the tremendously strong statements of Scripture on the subject and, on the other, to her own consciousness of unique and infinite obligation to the dying Saviour. Perhaps the most satisfactory expression of the Christian consciousness on the subject is to be found in the hymns of the Church, from the Te Deum down through Scotua Erigena and Fulbert of Chartres to Gerhardt and Toplady. See Schaff's _Christ in Song_.
A third line of development might be traced--the Practical--in martyrology, the history of missions, asceticism, and the like; and the spokesman of this branch of the truth is à Kempis, who, as Zöckler says, teaches his disciples to know poverty and humility as the roots of the tree of the Cross, labour and penitence as its bark, righteousness and mercy as its two principal branches, truth and doctrine as its precious leaves, chastity and obedience as its blossoms, temperance and discipline as its fragrance, and salvation and eternal life as its glorious fruit.
[6] When the Northern nations became Christian they transferred to the Cross the nobler ideas embodied in the mystic tree Igdrasil; and one of the commonest ideas of the mystical writers of the Middle Ages is the identification of the Cross as both the true tree of life and the true tree of knowledge.