The feast of the Most Precious Blood of our Lord was instituted in 1849 by Pius IX, but the devotion is as old as Christianity. The early Fathers say that the Church was born from the pierced side of Christ, and that the sacraments were brought forth through His Blood.
"The Precious Blood which we worship is the Blood which the Savior shed for us on Calvary and reassumed at His glorious Resurrection; it is the Blood which courses through the veins of His risen, glorified, living body at the right hand of God the Father in heaven; it is the Blood made present on our altars by the words of Consecration; it is the Blood which merited sanctifying grace for us and through it washes and beautifies our soul and inaugurates the beginning of eternal life in it."
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O God, who by the Precious Blood of your Only Begotten Son have redeemed the whole world, preserve in us the work of your mercy so that, ever honoring the mystery of our salvation, we may merit to obtain its fruits. Through Christ our Lord. Amen.