1. We have seen that the human meaning of all other aspects of Jesus’ redemptive act can be understood in relation to his free acceptance of death (22‑G). We have also seen how the Last Supper as a human act was related to the events of the following day and to the resurrection. It remains to show how the Mass and the sacrifice of the cross, considered as human acts, are one and the same, differing only in the manner of offering.2
The General Instruction of the Roman Missal (Introduction, 2) recalls that the Council of Trent teaches definitively that the Mass is a true sacrifice (see DS 1739–42/938–39). The Instruction also quotes Vatican II on the point that our Lord instituted the Eucharist to perpetuate the sacrifice of his body and blood through the centuries until he comes again (see SC 47). The doctrine is expressed in the prayers of the Mass. The Instruction then states: “In this new missal, then, the Church’s rule of prayer corresponds to the Church’s enduring rule of faith. It teaches us that the sacrifice of the cross and its sacramental renewal in the Mass are one and the same, differing only in the manner of offering. At the Last Supper Christ the Lord instituted this sacramental renewal and commanded his apostles to do it in memory of him. It is at once a sacrifice of praise and of thanksgiving, a sacrifice that reconciles us to the Father and makes amends to him for the sins of the world.”
2. As spiritual realities, choices last (2‑E). The choice which served as the vehicle, as it were, of Jesus’ free acceptance of death—an act sufficient in itself to bind humankind to God forever—did not cease with the end of the Last Supper or with his death. It still remains a determinant of his glorious human identity (see Heb 9.11–12, 24–28; 10.5–14). The choice which he executed by going to Jerusalem, eating the Passover, and accepting the consequences still exists (cf. S.t., 3, q. 22, a. 5).
3. Eating the Passover and celebrating the Eucharist at the end of the meal were religious acts of Jesus in which the Twelve also shared. Except for Judas, they were Jesus’ friends, and, while not clearly understanding what he was doing, they wanted to be with him in it. By cooperating with him, through receiving and consuming his body and blood, they took part in his redemptive act.
The eucharistic sacrifice is a sign, for it does signify the bloody consequences of Jesus’ choice. But the sign here is not merely a symbol with a purely cognitive relationship to what it symbolizes. The first Eucharist is Jesus’ very carrying out of the choice in making which he concretely accepted death. Thus the sign expresses the existential reality.
4. As part of his eucharistic action, Jesus includes the command: “Do this.” Thus he brought it about that the Mass in each of its performances concretely actualizes the eucharistic sacrifice he offered. In other words, in commanding the repetition of his eucharistic action, Jesus establishes a real, existential relationship between his own choice, which led to his death, and the act of the priest consecrating in the Mass. In short, the Mass today continues to carry out the basic, redemptive commitment of Jesus. This is done now in a different manner than on Good Friday, but its present carrying-out is really part of what Jesus was doing then, because the priest does now what Jesus then told him to do (see S.t., 3, q. 64, a. 5, ad 1; q. 78, a. 1; q. 83, a. 1, ad 2, 3).
5. Thus, as Vatican II teaches (see SC 47), the Mass perpetuates the sacrifice of the cross until Jesus comes again. The Mass makes the sacrifice of the cross present so that we can share in it. The faithful ought to offer Jesus not only through the priest but with him, and so learn to offer themselves as well (see SC 48).
6. It follows that all of Christian life proceeds from and prepares for the Eucharist (a point to be discussed more fully in chapter thirty-three). Christians live in order to have prayers and works, joys and sufferings, to bring to the Offertory; having known Jesus in the breaking of the Bread, Christians come forth from Mass and enter into other activities in order to love and serve the Lord. In the Mass Christians are united with Jesus in his sacrificial act, which thus should be the overarching act of each Christian’s life as a whole.
It is in the Mass that persons already Christian by baptism become fully joined to Jesus by cooperating in his human act and thus linking their own lives (made up of their own acts) with his. The Eucharist contains our Lord himself:
Through his very flesh, made vital and vitalizing by the Holy Spirit, he offers life to men. They are thereby invited and led to offer themselves, their labors, and all created things together with him.
Jesus’ redemptive act is community forming. By faith one accepts God’s communication of redemptive love. This love requires one to live as God’s children should live.
Hence the Eucharist shows itself to be the source and the apex of the whole work of preaching the gospel. Those under instruction are introduced by stages to a sharing in the Eucharist. The faithful, already marked with the sacred seal of baptism and confirmation, are through the reception of the Eucharist fully incorporated into the Body of Christ.
Thus the Eucharistic Action is the center of the congregation of the faithful over which the priest presides. So priests must instruct them to offer to God the Father the divine Victim in the sacrifice of the Mass, and to join to it the offering of their own lives. (PO 5; translation amended)
2. See Brian Byron, A Theology of Eucharistic Sacrifice, Theology Today, 35 (Hales Corners, Wis.: Clergy Book Service, 1974), 37–70, for a generally helpful treatment with a good bibliography. Byron lacks understanding of the lastingness of human acts and is unable to explain the unity of Calvary and the Mass in fully existential categories, and so unfortunately reduces the Mass to a symbolic likeness of the one sacrifice.