One may perceive three stages in this chief phase of mediaeval intellectual progress, consisting in the appropriation of Latin Christianity: its first conning, its more vital appropriation, its re-expression, with added elements of thought. There were also three stages in the evolution of the outer forms of this same catholic mastery and re-expression of doctrine: first, the Scriptural _Commentary_; secondly, the _Books of Sentences_; and thirdly, the _Summa Theologiae_, of which Thomas Aquinas is the final definitive creator. The philosophical material used in its making was the substantial philosophy of Aristotle, mastered at length by this Christian Titan of the thirteenth century. In the _Summa_, both visibly as well as more inwardly and essentially considered, the Latin Christianity of the Fathers received an organically new form. Quite as impressive, more moving, and possibly more creative, than the intellectual recasting of the ancient patristic matter, were its emotional transformations. The sequence and character of mediaeval development is clearly seen in the evolution of new forms of emotional, and especially of poetic and plastic, expression. The intellectual transformation of the antique and more especially the patristic matter, was accompanied by currents of desire and aversion, running with increasing definiteness and power. As patristic thought became more organically mediaeval, more intrinsically part of the intellectual faculties of men, it constituted with increasing incisiveness the suggestion and the rationale of emotional experiences, and set the lines accordingly of impassioned expression in devotional prose and verse, and in the more serious forms of art. Patristic theology, the authoritative statement of the Christian faith, contained men’s furthest hopes and deepest fears, set forth together with the divine Means by which those might be realized and these allayed. As generation after generation clung to this system as to the stay of their salvation, the intellectual consideration of it became instinct with the emotions of desire and aversion, and with love and gratitude toward the suffering means and instruments which made salvation possible--the Crucified, the Weeping Mother, and the martyred or self-torturing saints. All these had suffered; they were sublime objects for human compassion. Who could think upon them without tears? Thus mediaeval religious thought became a well of emotion.