1666-1714. Lutheran theologian and devotional writer. He was educated at Wittenberg and afterward, through the influence of Philip Spener, became a teacher at Quedlinburg. He became identified with exponents of mystic and separatist tendencies and in 1696 published Die erste Liebe, a eulogy on the simplicity and poverty of the primitive church and a condemnation of what he considered the later addition of dogma and ecclesiasticism. The next year he was invited to Giessen as professor of church history, but finding himself out of sympathy with the school resigned and returned to his former position. There he wrote the monumental work, Unparteiische Kirchen-und Ketzer-Historie (1699-1700) in which he showed more impartiality to heresy than to the church. In this study of heretical movements, Arnold refused to accept as evidence the statements of hostile contemporaries and based his work on the writings of the sectarians themselves. This, with his presuppositions about the weaknesses of the orthodox position, led him to favor the separatists of various ages and caused controversies which forced him deeper into a mystical position. In 1704 he became pastor and inspector at Werben in Prussia and was reconciled with establishment Christianity. In 1707 he became inspector at Perleberg. In addition to his church history he wrote over fifty works and composed many beautiful religious songs, some of which are still used.