In the years 1515 and 1516, which bear traces of a more thoroughgoing study of Augustine and of the German mediæval Mystics, Luther began to find that he could not express the thoughts he desired to convey in the ordinary language of Scholastic Theology, and that its phrases suggested ideas other than those he wished to set forth. He tried to find another set of expressions. It is characteristic of Luther’s conservatism, that in theological phraseology, as afterwards in ecclesiastical institutions and ceremonies, he preferred to retain what had been in use provided only he could put his own evangelical meaning into it in a not too arbitrary way.(148) Having found that the Scholastic phraseology did not always suit his purpose, he turned to the popular mystical authors, and discovered there a rich store of phrases in which he could express his ideas of the imperfection of man towards what is good. Along with this change in language, and related to it, we find evidence that Luther was beginning to think less highly of the monastic life with its _external_ renunciations. The thought of predestination, meaning by that not an abstract metaphysical category, but the conception that the whole believer’s life, and what it involved, depended in the last resort on God and not on man, came more and more into the foreground. Still there does not seem any disposition to criticise or to repudiate the current theology of the day. The earliest traces of _conscious_ opposition appeared about the middle of 1516, and characteristically on the practical and not on the speculative side of theology. They began in a sermon on Indulgences, preached in July 1516. Once begun, the breach widened until Luther could contrast “our theology”(149) (the theology taught by Luther and his colleagues at Wittenberg) with what was taught elsewhere, and notably at Erfurt. The former represented Augustine and the Holy Scriptures, and the latter was founded on Aristotle. In September 1517 he raised the standard of theological revolt, and wrote directly against the “Scholastic Theology”; he declared that it was Pelagian at heart, and buried out of sight the Augustinian doctrines of grace; he lamented the fact that it neglected to teach the supreme value of faith and of inward righteousness; that it encouraged men to seek escape from what was due for sin by means of Indulgences, instead of exhorting them to practise the inward repentance which belongs to every genuine Christian life. It was at this interesting stage of his own religious development that Luther felt himself forced to oppose publicly the sale of Indulgences in Germany.