Thesis advisor: Richard R. Gaillardetz / For the Catholic Church, the Second Vatican Council serves as a compass regarding its purpose and direction for the third millennium. Lumen Gentium defines the Church as “a sacrament – a sign and instrument” of “communion with God and the unity of the entire human race.” As a sacrament of unity, the Church calls all “to this catholic unity of the people of God, which prefigures and promotes universal peace” (LG,1). Such catholic unity or catholicity is neither a given nor an abstraction. Catholicity requires the cooperation of human effort with divine grace for the reconciliation of all peoples. To remain faithful to this mission, the Church must first recognize how its own damaged sense of catholicity has resulted in turning brother against brother in the name of Christ. Every time Catholics participated in the homogenizing logics of domination, such as the latinization of Eastern Christians, the colonization of the global South, and current expressions of Eurocentric white supremacy, they have contributed to the woundedness that harms the Body of Christ. In each of these broken relationships, the Church has wandered from its original purpose to the extent that it has allowed itself to become corrupted by forms of power that are not shaped by the foolishness of the Cross (1 Cor 1:18). To transform our wandering back into journeying, the Church must rediscover the meaning and purpose of its catholicity for the third millennium. It must allow the cries of the wounded to reveal the lack of concrete human communion that first exists among the faithful. Only by working towards the healing of these relationships within the Church can it have integrity in preaching unity to the rest of the world. To cultivate this culture of encounter within, I argue that we must reimagine catholicity from an interstitial perspective. This perspective locates catholicity not only between the cultural differences of the Roman Catholic church, but also the ecclesial differences between the Western and Eastern churches of the Catholic communion. The “third space” that emerges at the interstices between faith communities becomes a space of encounter, not only forcing the enunciation of difference, but also the question and the nature of catholic unity amidst difference. Resisting both the centripetal temptation to assimilate difference into the whole and the centrifugal temptation to maintain difference at the peripheries, a reimagination of catholicity from an interstitial perspective emphasizes how the Church itself is a liminal figure, encouraging the faithful to respond more authentically to the call to exist spatially as leaven – transforming society from within - and temporally as pilgrim between the promise and the fulfillment. / Thesis (PhD) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Theology.