Sacred Scripture tells us that God has obtained the Church with His own blood (cf. Acts 28:28). According to the teaching of the Catechism of the Catholic Church:
The Church is born primarily of Christ’s total self-giving for our salvation, anticipated in the institution of the Eucharist and fulfilled on the Cross. “The origin and growth of the Church are symbolized by the blood and water which flowed from the open side of the crucified Jesus.” “For it was from the side of Christ as he slept the sleep of death upon the Cross that there came forth the ‘wondrous sacrament of the whole Church.’ ” As Eve was formed from the sleeping Adam’s side, so the Church was born from the pierced heart of Christ hanging dead on the Cross.
CCC 766, citing Lumen Gentium 3 and Sacrosanctum Concilium 5, and citing St. Ambrose, In Luc. 2, 85–89, PL 15:1666–68. …
