The Body of Christ has a history that may be mapped, discussed, and studied; it continues to suffer various indignities and worse until the End; and the teachings of its churches undergo various changes.
Bede points to Peter’s exaltation (historical and, it seems ongoing) over the other apostles as a sign: that those who would enter the Church and be saved must remain in the faith of Peter and in the fellowship of the Church.
When Christians come together to serve the Lord in works of mercy, something very beautiful happens. Our eyes move from our all-too-present divisions to touching Christ in one of the only ways we can together: as he comes to us in the poor.