The connections between Martin Luther and Weimar are closer than it might seem. Luther visited the city quite often between 1518 and 1540. Since 1485, Weimar belonged to the realm ruled by Ernestine Line, which also included the Residence in Torgau and the university town of Wittenberg. Luther spoke here at the court of his rulers, Electoral Prince Johann des Beständigen (John the Constant) and later Johann Friedrich des Großmütigen (John the Magnanimous). He consulted with those responsible about the advancement of the Reformation and also took instruction in the same.

Elector Johann Friedrich also brought Lucas Cranach to Weimar. During his visits, Luther preached at the City Church of St. Peter and Paul many times. From 24 until 26 October 1522 he preached four times altogether at the Weimar castle church and the City Church. The pamphlet "About secular powers and to what extent one should be obedient" or the so-called "Two Kingdoms Doctrine" of 1523 originated here during these sermons and has shaped the protestant understanding of the relationship between faith and politics ever since. In the City Church the triptych by Lucas Cranach the Younger illustrates Luther's teachings. Among other places, the Franciscan monastery at the Palais was one of the places he stayed, and nowadays a plaque there commemorates that fact.