Consider: The church both learns and becomes what it truly is when it gathers to worship. Worship tells the story of God's salvation history and invites God's people into it. By doing so, the church offers the world both a stern warning and a hopeful promise. These are three of the key insights that animated the work of Jean-Jacques von Allmen, a Swiss Reformed pastor and professor who is among the most admired liturgical theologians of the twentieth century. Yet his work is largely and lamentably unknown to most worship leaders. In this book, Ron Rienstra provides an introduction to this important thinker. He offers methodological and biographical context and then explores von Allmen's most generative insights concerning the church as it engages in its most foundational activity: worship. Viewed through the lens of the Nicene marks, Rienstra's exploration yields the outlines of a "liturgical ecclesiology" a way to help the church think more deeply about its identity and to help its leaders shape the worship they prepare and lead today.