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Theological disputes

In the beginning of 1521, Melanchthon defended Luther in his Didymi Faventini versus Thomam Placentinum pro M. Luthero oratio (Wittenberg, n.d.). He argued that Luther rejected only papal and ecclesiastical practises which were at variance with Scripture. But while Luther was absent at Wartburg Castle, during the disturbances caused by the Zwickau prophets, Melanchthon wavered.

The appearance of Melanchthon's Loci communes rerum theologicarum seu hypotyposes theologicae (Wittenberg and Basel, 1521) was of subsequent importance to the Reformation. Melanchthon discussed the "leading thoughts" of Paul's Letter to the Romans and used this platform to present a new doctrine of Christianity; one where faith in God was more important than good deeds. Loci communes contributed to the gradual rise of the Lutheran scholastic tradition, and the later theologians Martin Chemnitz, Mathias Haffenreffer, and Leonhard Hutter expanded upon it. Melanchthon continued to lecture on the classics.

On a journey in 1524 to his native town, he encountered the papal legate, Cardinal Lorenzo Campeggio, who tried to draw him from Luther's cause. In his Unterricht der Visitatorn an die Pfarherrn im Kurfürstentum zu Sachssen (1528) Melanchthon presented the evangelical doctrine of salvation as well as regulations for churches and schools.

In 1529, Melanchthon accompanied the elector to the Diet of Speyer. His hopes of persuading the Holy Roman Empire to recognize the Reformation were not fulfilled. A friendly attitude towards the Swiss at the Diet was something he later changed, calling Huldrych Zwingli 's doctrine of the Lord's Supper "an impious dogma ".