Bugenhagen began to read Luther's other writings; and he was especially charmed with his exposition of the difference between the Law and the Gospel, and of the doctrine of justification by faith. Persecution soon began, instigated by the bishop of Camin. Bugenhagen, who earnestly desired to see the places whence the light had come, betook himself to Wittenberg, arriving there in 1521, shortly before the departure of the reformer to Worms. The Pomeranian was joyfully received by Luther and Melanchthon, who thenceforth usually called him 'Pomeranus.' His desire was to be a student, not a teacher; but having begun, in his own room, to explain the Psalms to his countrymen, he did this with so much clearness, such unction and evangelical life, that Melanchthon requested him to give the course publicly. He now became one of the professors of the University, and at the same time pastor of the parish church. He was afterwards (1536) appointed superintendent-general. Melanchthon and Pomeranus completed, each on his special side, the work of Luther. Melanchthon did so in the scientific sphere, by means of his classical culture, and in the political sphere by his discretion. Pomeranus, though undoubtedly inferior to both of them, had great experience and much knowledge of men, and he possessed at the same time gentleness and firmness, abundance of tact and a practical turn of mind, and to all these qualities he added energetic activity. He was thus enabled to render great services in all that related to ecclesiastical organization.[482] There was hardly an important church in whose formation his assistance was not sought. We have already met with him in Denmark.[483] We have elsewhere seen how the Gospel had been brought to Erfurt by Luther and by Lange, how Frederick Myconius, converted partly by Tetzel's excesses, had preached the Gospel at Zwickau, and how the word had renovated other towns in connection with Wittenberg. When a friend of Luther, Nicholas Hausmann for instance, was called to some place for the work of the Reformation, and came to ask the great doctor's advice, the latter answered: 'If you accept the call, you will make enemies of the pope and the bishops; but if you decline it, you will be the enemy of Christ.' This was enough to induce them to enter upon the work.[484] The evangelical doctrine had been publicly preached at Frankfort-on-the-Main by Ibach, just after the famous diet of Worms. Assemblies of evangelical deputies had been held there in June, 1530, December, 1531, and May, 1536, and this town had joined the alliance of Smalkalde.