Heading South from Potsdam you reach Lutherstadt-Wittenburg. Here Martin Luther is said to have nailed his 95 Theses to the door of the Castle Church 500 years ago. Thus began a process of sundering sect from sect that continues to this day. Little things mean a lot when it comes to religion.
You should read the 95 theses or at least a good biography. A lot to admire here - a man who spoke truth to power in more than one significant way. Also, as are we all, flawed.
L-W is the Vatican or Jerusalem of Protestantism. This is made clear by the number of tour groups and the availability of Luther socks in the souvenir shops. They are embroidered with Luther's famous line: "Here I stand, I can do no other."
Ave frater, ave.