Johan Kemper

Johan Kemper was a 17th-century Polish figure who began his life as a Sabbatean Jew, known as Moshe ben Aharon Ha-Kohen of Kraków or Moses Aaron. Born in 1670, his early life was marked by adherence to the Jewish faith, with a particular interest in the mystical teachings of Kabbalah. However, his spiritual journey took a significant turn due to his involvement with the Sabbatean movement, which centered on the belief in Sabbatai Zevi as the messiah.

Kemper's conversion to Lutheran Christianity, where he took the name Johann Christian Jacob, was a pivotal event in his life. This change occurred after he became disillusioned with the Sabbatean prophecy, specifically the prediction by Zadok of Grodno that Sabbatai Zevi would return in 1695/6, which ultimately did not come to pass. The failure of this prophecy, coupled with his deepening studies in Kabbalah, led Kemper to reevaluate his faith, resulting in his conversion. He passed away in 1716, with the extent of his continued observance of Jewish practices after his conversion remaining unclear.