According to his own statement, his Christian friends, and especially his study of the history of Israel, led him to Christianity. He was baptized as a member of Evangelical Church in Prussia on May 28, 1855 in the St. Peter's Church of Büßleben (now a locality of Erfurt), receiving the name "Paulus Stephanus." In later years he celebrated May 28 as his "second birthday". He became librarian of the Royal Library in Erfurt and secretary of the Academy in Erfurt in the following year. He remained in Erfurt till 1859. King Frederick William IV bestowed the title of professor on Cassel in recognition of his loyal labors. In 1860 he removed to Berlin, where he was a teacher at a gymnasium for a short time, and occupied himself with literary work. He was briefly editor of the official "Deutsche Reform". He delivered public lectures, which drew increasingly large audiences, both Jews and Gentiles. These lectures made him known throughout Berlin and the country.