Jesus Christ abolished all sacrifices but that of the Cross. He died once, and can suffer now no more. Still, His death can be set forth in commemoration of Him, and is set forth in the Mass. That this setting forth is a real sacrifice has always been the teaching of the Church. It is the fulfillment of the prophecy spoken by Malachias:
"From the rising of the sun even unto the going down of the same My name is great among the Gentiles, and in every place there is sacrifice, and there is offered to My name a clean oblation; for My name is great among the Gentiles, saith the Lord of hosts." (Malachias 1)
This sacrifice and clean oblation must be the Mass; if it is not, the prophecy has failed, for there is no rite among the Gentiles or nations which claims this title. Moreover, the Apostle says in the Epistle to the Hebrews: "We have an altar whereof they who serve the tabernacle have no power to eat." Now, if we have an altar we must have a sacrifice, for there is no altar with out a sacrifice (15). The only use of an altar is for the offering of sacrifice. If, then, we have such an altar we must have a sacrifice, and the only rite which lays claim to this character is the Mass.
We know the Mass is a sacrifice, but how the Mass is a sacrifice is a much more difficult question. Learned men have made many learned explanations of the matter, which belong properly to the science of theology. We will content ourselves with the answer suggested in the Catechism. You remember the question, "What is a Sacrifice?" "A sacrifice is the offering of an object by a priest to God alone and the consuming of it to acknowledge that He is the Creator and Lord of all things." Hence, in the sacrifice of the Cross we had the "offering" by our Lord, our High Priest. The "victim" or "object" offered was Himself, the price of our redemption. "Consume" means to destroy by separating into parts, and Christ's death was a bloody death, the separating of His soul from His body caused by the shedding of His precious blood. Now, Christ died once, and can die no more. After His resurrection, soul and body, body and blood are reunited, never again to be separated. How, then can there be a consumption of the Victim in the Holy Sacrifice of the altar? The explanation suggested in the Catechism is contained in the question: "Is there any difference between the sacrifice of the Cross and the sacrifice of the Mass?" "Yes; the manner in which the sacrifice is offered is different. On the Cross Christ really shed His blood and was really slain; in the Mass there is no real shedding of blood nor real death, because Christ can die no more; but the sacrifice of the Mass through the separate consecration of the bread and wine represents His death on the Cross." That is to say, "Jesus Christ is whole and entire both under the form of bread and under the form of wine," but when the bread is consecrated He "appears" under the form of bread, which is the "figure" of His body, and when the wine is consecrated He "appears" under the form of wine, which is the "figure" of His blood. In other words, He is shown forth on the altar under the guise he bore when His pale body hung upon the Cross and His precious blood bedewed the ground. Moreover, this condition of our Lord suggests another "consumption." Jesus Christ is reduced to a condition which is equivalent to death. He who is so great and glorious in heaven appears as a piece of bread and a drop of wine. When a man dies he loses his natural bodily powers, but Jesus Christ hides even His human form under the sacramental veils, and becomes what the sacrifices of old were to them that offered them, namely, food and drink. Therefore, we say that the separate consecration of the bread and wine shows forth the death of the Lord, and that transubstantiation, or the fact that Christ is really and substantially present under the forms of bread and wine, is equivalent to the destruction or consumption of the Victim.
"The Incarnation was a descent which had man} degrees. He emptied Himself by veiling His glory; He took the form of a servant; He was made man; He humbled Himself; and that to death; and to die in ignominy. Here are six degrees of humiliation. And as if these were not enough. He perpetuates His humility in the Blessed Sacrament, and places Himself in the hands of His creatures, and is bid, morning by morning, by their word to be present upon the altar; and is by them lifted up, and carried to and fro, and, in the end. He is received by the worthy and by the unworthy." (Manning, "Eternal Priesthood," Chapter 2)
The Mass is the same Sacrifice as that of the Cross, because the essential parts of the Sacrifice are the same. That is to say, one Sacrifice is the same as another, when we have the same priest, the same victim and the same purpose for which the offering is made. Now, in the Mass, we have the same priest as in the Sacrifice of the Cross. The Catholic priest is a priest only inasmuch as he represents Jesus Christ and shares in His eternal priesthood. He speaks in the name of Christ and acts in His name. Therefore, he says, "This is My body; this is My blood." Secondly, we have the same Victim, for we believe that when Jesus Christ said at His Last Supper, "This is My body," He meant what He said, and He was powerful enough to make His meaning good. Therefore, The Victim in the Mass is none other than Jesus Christ, the Victim on the Cross. Thirdly, we have the same ends or purposes, for (a) Jesus Christ died to honor and glorify God. He represented the whole human race, and gave to His Father that infinite worship which only God could give to God. (b) He gave infinite thanks for the graces bestowed on the whole world, (c) He made infinite satisfaction to the majesty of God, offended by sin, and He washed away with His blood all the guilt of man kind, (d) He merited and obtained all the graces and blessings, natural and supernatural, for the human race.
Now, in the Mass we have these four ends. For, 1st The Mass as a Sacrifice is the supreme act of worship testifying to God's almighty dominion. This is the chief end of the Mass, as it is of all sacrifice. 2rd The Mass is a Eucharistic Sacrifice. "Eucharist" is a Greek word meaning "Thanks giving." The Mass is a thank-offering to God for all the benefits bestowed on the whole world. 3rd It is a Sacrifice for sin. By the Sacrifice of the Cross, Christ made atonement for the sins of the world, once for all. But we have to co-operate with God to work out our salvation, because, though atonement has been made, we are not saved without our own will. We have to perform stated conditions to obtain a share in that redemption. For instance, the American Revolution won for the citizens of this Republic a right to share in its government. But no man can exercise that right, say, by voting, until he has observed certain conditions, say, living for a certain time in a certain district and registering his name after the manner prescribed by law. In somewhat the same way the Sacrifice of the Cross has redeemed us all from sin and given us a place in the Christian republic, or the Kingdom of God, but we cannot take that place or enjoy the rights thereof until we have performed certain conditions. Now, the Mass applies the merits of the original Sacrifice to our souls. It is continued from day to day because men's needs shall last to the consummation of ages. The inexhaustible character, the universal extent and the completeness of the Sacrifice of the Cross are thus made manifest by the never-ceasing offering of the Sacrifice of the Mass by which the fruits of the Passion are applied to men. From the rising of the sun even to the going down of the same there is offered a clean oblation. Lastly, 4th The Sacrifice of the Mass obtains for us other graces and blessings merited by Jesus Christ. It is the means which He instituted that they should come to us.
The priest has the power to apply the fruits of the Sacrifice for any person he wills. When we ask to have Mass said for our intention we mean that the priest will make our intention his own and apply the special fruits of the Sacrifice as we desire.
- taken from The Mass, by Father Peter Christopher Yorke