Four decades have passed since the publication of Gerhard Lenski’s The Religious Factor. While generally regarded as a classic in the sociology of religion, the book has had a curious history, largely because of the interest it generated in differences between Protestants and Catholics. In this paper I provide an alternative reading of The Religious Factor’s impact on sociology of religion that points to its larger theoretical implications. I argue that the book should be understood in relation to continuing debates about the classification of religious traditions, differentiation among socioreligious groups, intergroup relations among religious traditions, and friendship ties within religious communities. Through understanding these contributions, the book's legacy as well as continuities and new opportunities in the study of religion can be appreciated.