The article shows how America’s nineteenth-century Benedictine missionaries adopted a sacramental vision of evangelization. In particular, the study posits an intriguing, albeit qualified parallel between Vatican II’s articulation of the church as sacrament (Lumen gentium no. 1) and the thought of two abbots at the headwaters of the American Benedictine movement: Boniface Wimmer (1809-1887) and Martin Marty (1834-1896). These pioneer monks understood the monastery as an ecclesial sacramentum, or in the words of Lumen gentium, as an instrument and sign of evangelization. In support of this thesis, two significant ideas arise in the abbots’ distinct yet complementary visions for monasticism in America: (1) the role of the Benedictine vow of stabilitas (RB 4.78, 58.17), and (2) the role of the local Catholic community within the universal church. Overall, the study demonstrates how America’s earliest Benedictines anticipated Vatican II’s renewal of the perennial call for Catholics to be a light to the nations.