In an era when intellectuals were celebrities, Dr Nathan Birnbaum was a household name across the Jewish world. When one of the most famous secular Jews of the age rediscovered Hashem, assimilationists were confounded and Orthodoxy received a shot in the arm. Rabbi Efraim Zalman Galinsky and Gedalia Guttentag trace the impact of one of the modern era’s most famous Baalei Teshuva.