His experiences at the convent led him to the perception of those principles which formed the groundwork of his preaching as a Reformer. From his exemplary conduct there, and his wonderful and active conversion, he was compared to St. Paul. In quite another sense he resembled the great Apostle. The latter, when a Pharisee, had laboured to justify himself before God by the law and the prophets. 'O wretched man that I am,' Luther there must have exclaimed of himself, and afterwards looking back on his experiences, have counted all as 'dung and loss' in order to be justified rather by faith through the grace of God and the Saviour, and to become free and holy.
Just as, meanwhile, inside the Catholic Church, the laws, dogmas, and School theories relating to the means of salvation, were never able to supplant entirely the thought of the simple testimony of the Bible, and of the Church's own confession of God's forgiving love and His redeeming and absolving grace, or to prevent simple, pious Christians from seeking here a refuge in the inmost depths of their hearts, so now, at this very convent of Erfurt, where Luther's inward development in those theories and dogmas had reached so high a pitch, he received also the first serious impressions in the other direction. They found with him a difficult and gradual entrance, from the energy and consistency with which he had taken up his original standpoint. But with all the more energy, and with perfect consistency, did he abandon that standpoint, when new light dawned upon him from his new conception of the truth.
Luther's teacher at the convent, by whom we shall have to understand the superintendent of the novices, had already made a deep impression upon him, by reminding him of the words of the Apostles' Creed about the forgiveness of sins, and representing to him, what Luther had never ventured to apply to himself, that the Lord himself had commanded us to hope. For this he referred him to a passage in the writings of St. Bernard, where that fervent preacher, imbued though he was in his theology with the Church notions of the middle ages, insists on the importance of this very faith in God's forgiveness, and appeals to the words of St. Paul that man is justified by grace through faith. Remarks of this kind sank into Luther's mind, and took root there, though their fruit only ripened by degrees. Of his teacher Arnoldi, also, he spoke with admiration and gratitude, for the comfort he had known how to impart to him.