68 You also realize, Venerable Brothers, that the Eucharist is reserved in churches or oratories to serve as the spiritual center of a religious community or a parish community, indeed of the whole Church and the whole of mankind, since it contains, beneath the veil of the species, Christ the invisible Head of the Church, the Redeemer of the world, the center of all hearts, "by whom all things are and by whom we exist." (70)
Source: Mysterium Fidei (Vatican.va)