Central to Vatican II’s deliberations on the church was a fundamental rediscovery: the church’s origin in the mystery of the Trinity. How this rediscovery permeates and shapes the council’s ecclesial vision is what this article addresses. Four leitmotifs exemplify the expanded horizon for the council’s understanding of the church that this rediscovery afforded: church as mystery, as communio, as mission to the world, and as community of dialogue.