This article addresses the issue of Luke's authorial purpose for the composition of the Luke-Acts literature. Observing that existing theories are inadequate in that they fail to provide a comprehensive cohesive program for the literature's content and are anachronistically complex, the article suggests an authorial purpose paradigm natural to the early Jesus movement's status as a newly emerging society. Through application of Berger and Luckmann's sociology of knowledge models, this article argues that reading Luke-Acts as the author's legitimation of the Jesus movement's social world is a valid, even preferred reading of the literature. By tracing key elements in the development of Luke's legitimation conceptual machinery, the social conflict background is established-further indicating that it is the social conflicts that motivated the document's writing and organized its content. This article lays a foundation for Luke's legitimating strategy, which was in response to a purity conflict theme. It is argued that this was Luke's primary purpose for writing Luke-Acts.