Much of Lenski's earliest work dealt with the sociology of religion and culminated in the publication of "The Religious Factor". He defines religion as "a system of beliefs about the nature of force(s) ultimately shaping man's destiny and the practices associated therewith, shared by the members of a group. A reviewer in "Commentary" described the book as a "major achievement" in an often-neglected subfield, and Robert Wuthnow has referred to this volume as "arguably one of a handful of 'classics' among contributions by American sociologists to the social scientific study of religion."