When a priest pronounces the words of Eucharistic consecration at Mass, the bread and wine, by the power of the Holy Spirit, are changed into the Body and Blood of Christ, which were given for us in sacrifice.
At the Last Supper, Jesus’ words and power made Him really and substantially present under the outward appearances of bread and wine which He gave the Apostles to eat; so, they actually received Jesus in that meal and were united with Him. This made the Apostles one with our Lord and all that He did. They shared in both His gift of Himself to His Father on the Cross and in the Father’s gift of life to Jesus in the Resurrection. Later, the Apostles gave Jesus Christ to the People of God in the Holy Eucharist.
In the celebration of the Mass, the Church re-creates the Last Supper by bringing followers of Jesus together and recalling, through readings and prayers, what God has done for His people. Then the priest repeats what Jesus said at the Last Supper, and himself gives the consecrated bread and wine, which is now Jesus’ Body and Blood, to the people.
Many Protestants object to the Catholic priesthood, claiming that it counters what is written in the New Testament Letter to the Hebrews. The passage referred to says: “And by that will we have been sanctified through the offering of the body of Jesus Christ once for all. And every priest stands daily at his service, offering repeatedly the same sacrifices, which can never take away sins. But when Christ had offered for all time a single sacrifice for sins, he sat down at the right hand of God, then to wait until his enemies should be made a stool for his feet” (Hebrews 10:10–13).
How does the Catholic Church interpret these words? The Catholic Church teaches that the Holy Sacrifice of the Mass does not involve Christ’s Death for us anew. Rather, it is a participation in the one sacrifice of Christ on Calvary, in an unbloody manner, the benefits of which continue into eternity. Jesus continually lives to make intercession for us, offering to the Father, on our behalf, Himself, given for us on the Cross.
“But he holds his priesthood permanently, because he continues for ever. Consequently he is able for all time to save those who draw near to God through him, since he always lives to make intercession for them.” (Hebrews 7:24–25).
Every ordained Catholic priest participates in the one priesthood of Christ, which alone can take away the sins of the world. When the priest pronounces the words of Eucharistic consecration, he is said to do so in persona Christi, that is, in the person of Christ. It is really Christ speaking through the words of His priest, when the priest says, “This is my Body,” and “This is my Blood.” The Old Testament sacrifices could never take away sins, but the sacrifice of Jesus on the Cross can. We participate in this sacrifice when we participate in the Holy Sacrifice of the Mass over which an ordained priest presides.