How freely can salvation be offered to people? How do Law and Grace find balance? What influence does Federal Theology have on the overall theological enterprise? How does a confessional church interact with both the civil government and other religious communions? These are the questions roiling the twenty-first century-church; these were the questions threatening to splinter the Scottish church in the early eighteenth century. In those earlier days of mounting theological confrontation within the Scottish church, Ebenezer Erskine–a parish minister renowned for his evangelistic zeal–had a major role to play. Through this examination of the theology and ministry of Erskine, one therefore gains not only a deeper understanding of a man critically important within Presbyterian history, but also insight into the pressing theological disputes of the day. By analyzing Erskine’s contributions to ongoing theological discussion, greater clarity is gained on the development of Federal Theology; on the root causes of the Marrow controversy; and on the challenges involved as increasing religious diversity penetrated lands once dominated by national churches. In these areas and more, Erskine serves both to illuminate an obscure era and to refine modern understandings of still controversial theological issues.