"One body, many members" is the New Testament's own model, and Christianity has spent two thousand years arguing about whether the body is visible or invisible. Catholic and Orthodox ecclesiology identifies the church with a concrete institution and apostolic succession; classical Protestantism distinguishes the invisible church of true believers from any visible organization; congregationalists locate the church in the local gathering. Roughly 45,000 denominations exist, and the ecumenical movement of the last century is the attempt to take the metaphor seriously again.