At the Mass, the priest says, "Pray, brethren, that our sacrifice may be acceptable to God, the almighty Father," to which the parishioners respond, "May the Lord accept the sacrifice at your hands." Why do the priest and the parishioners mention a "sacrifice?" They say this because the Mass is a real sacrifice (CCC 1365).
God created Adam and Eve in the state of grace, but because they sinned, they lost the grace that made their souls holy and pleasing to God and gave them a right to enter heaven (CCC 399-400). No matter what people did afterwards, they could not make up for their sinfulness. So Jesus, who was God the Son, the Second Person of the Trinity, born of the Virgin Mary, suffered and died (Matt. 27:26-50; Mark 15:15-37; Luke 23:26-46; John 19:1-30). When Jesus experienced His Passion and death, He offered up this suffering and death as a sacrifice, and God the Father accepted this act as a fitting sacrifice to redeem mankind (or buy back the gift of grace that had been lost), because the sacrifice of Christ pleased the Father more than sin displeased Him. Because of this sacrifice, grace was once again made available to all mankind, and would be applied to those who would believe in Christ and be baptized (CCC 1226-1228). This is necessary in understanding the Mass.
A sacrifice is the offering of a gift to God, in which the gift is in some way destroyed. The gift is a sign of adoration or devotion, acknowledging that God is the Creator and Lord of all creatures. A sacrifice often brings down certain benefits or blessings from God. The gift that is destroyed is called a "victim", and the one who offers the gift for sacrifice on behalf of all the people is called a "priest". In the Sacrifice of the Mass, Jesus is both priest and victim, just as he was on the cross. He was the sacrifice that was offered (victim), and the offering of that sacrifice was made by Himself (priest), who continues to offer Himself through the words and actions of His human priests.
This is how it works: The separation of the blood of Christ from His body caused His sacrificial death on Mount Calvary 2000 years ago. When the bread and wine are consecrated at the Mass into the body and blood of Christ (CCC 1376), the separate consecration of bread and wine re-enact that separation of the body and blood of Christ, and therefore Christ's death occurs just as it did on Calvary.
Although Jesus suffered and died once (Heb 9:12, 10:10) and offered Himself once (Heb 9:28, 10:12, 10:14), God makes that same sacrificial offering present at every Mass (CCC 1366). Though the sacrifice occurred 2000 years ago, the sacrifice made at the Mass through the separate consecration of bread and wine is the same sacrifice made by Jesus on Calvary (CCC 1367). So we are witnessing the actual death of Jesus at the Mass. As St. Paul wrote about the Mass, "As often as you shall eat this bread and drink this cup, you proclaim the death of the Lord" (1 Cor 11:26). This is difficult to understand, but it should be thought of in this way––a movie is shot only once, but it is seen repeatedly, in many different times and places, as many times as the movie is shown. That is the way the Mass works. Although Jesus died once, God makes that same death occur at every Mass, in a very mysterious way.
Although the Sacrifice of the Mass and the Sacrifice on the Cross is one and the same sacrifice, the manner of offering is different. On the Cross, Christ's blood was really shed, He really died, and the sacrifice made satisfaction for the sins of mankind. At the Mass there is no real shedding of blood, no death, and the satisfaction is not made, but applied, because Christ's suffering, death, and satisfaction occurred 2000 years ago and cannot occur again.
At the Last Supper, Jesus said the first Mass when He changed bread and wine into His own body and blood (Matt 26:26-29; Mark 14:22-25; Luke 22:17-20; 1 Cor 11:23-25). He then instructed His apostles to continue to offer the Mass by saying, "Do this in memory of me" (Luke 22:19; 1 Cor 11:25), which can also be rendered, from the original Greek, as "Offer this as my memorial sacrifice." So the Church has in every age offered the Mass, adding and changing prayers and actions throughout the years.
We offer the Mass to adore God, give Him thanks, satisfy His justice, and ask for blessings. Through the Mass, God bestows many blessings upon those at Mass, the whole Church, and even the entire world. These blessings may be increased or decreased depending upon the disposition of each person at Mass, and with the fervor and devotion with which he assists (prays the prayers, sings, and participates) at Mass. It is through the Mass that God applies the fruit of His redemption to our souls.
St. Paul said, "Now you are Christ's body, and individually members of it" (1 Cor 12:27). The Mass is the sacrifice of the whole Christ, the Mystical Body, or the Church (CCC 1368). Christ offers us up with Himself, our prayers, works, and sufferings in union with His, so that we might be offered as a "living sacrifice" (Rom 12:1).
Christians should show up early for Mass, in order to pray and offer up the Mass for any intentions. We should pray the prayers and sing the songs, meditating upon all the words we speak and sing. Most importantly, we should pay close attention to what is happening at the consecration, because that is where the sacrifice of Jesus occurs. Above all else, we should assist reverently and devoutly at the Mass, because that is when we receive the greatest blessings and graces. So why should we go to Mass often, even daily?
Because, as St. Lawrence Justinian said, "There is no prayer or good work so great, so pleasing to God, so useful to us as the Mass." St. John Vianney said, "Put all the good works in the world against one Holy Mass, they will be as a grain of sand beside a mountain."
For many years, a poor farmer attended daily Mass. While walking to church one cold morning, he heard footsteps behind him. He turned around and saw his guardian angel with a basket full of roses. "See," said the angel, "these roses represent each step you have taken on the way to Mass, and each rose represents, too, a glorious reward which awaits you in heaven. But far, far greater are the merits you have gotten from the Mass itself."