It was at about the time that Kepler left Latin school to enter Adelberg that he first became aware of a potentially explosive rift in the Protestant world. He heard a sermon in Leonberg given by a young deacon who spoke vehemently and at length against the Calvinists. Twelve-year-old Kepler went away deeply worried about this harsh controversy between those who adhered to slightly different confessions of the same faith. At the age of thirteen, he wrote a letter requesting that the University of Tübingen send him copies of Martin Luther's disputations. Kepler decided to make it a practice, whenever he heard a preacher or lecturer argue about the meaning of the Scriptures, to consult the passages himself rather than take anyone's word for what they meant. He usually decided that both interpretations had good points. This was not a healthy attitude for a young man who was hoping someday to find himself in a Lutheran pulpit - indeed for anyone wanting to survive unscathed in the political/religious milieu of the late sixteenth and early seventeenth centuries. Rather than win friends in both camps, it was likely to make enemies all round. As Kepler recalled his youthful inclination to see all sides of an argument: "There was nothing I could state that I could not also contradict." It was a gift, and sometimes a curse, that would remain with him all his life.

— Tycho and Kepler by Kitty Ferguson (24%)