74. As for unity of worship, the Catholic Church has had seven sacraments, neither more nor less, from her beginning right down to the present day. Jesus Christ left her these sacraments as a sacred legacy, and she had never ceased to administer them throughout the Catholic world and thus to feed and foster the supernatural life of the faithful.(source - official Vatican website)
75. All this is common knowledge, and it is also common knowledge that only one sacrifice is offered in the Church. In this Eucharistic sacrifice Christ Himself, our Salvation and our Redeemer, immolates Himself each day for all of us and mercifully pours out on us the countless riches of His grace. No blood is shed, but the sacrifice is real, just as real as when Christ hung from a cross of Calvary.
I. Exactly Seven Sacraments - 12th Century not 1st Century
As for J23's claim "As for unity of worship, the Catholic Church has had seven sacraments, neither more nor less, from her beginning right down to the present day," the claim is so historically untenable as to be naive at best. The "exactly seven sacraments" idea is the product of the 12th century, with Peter Lombard receiving the credit or blame for that doctrinal innovation (with Otto of Bamberg sometimes being given some secondary credit).
II. One Sacrifice - Many Sacrifices - Repetition - Perpetuation
J23's claim that "only one sacrifice is offered in the Church" has become popular these days among Roman Catholic apologists. Indeed, it is so emphasized that one can scarcely find a Roman Catholic these days who will acknowledge the concept of the "sacrifices of the mass" (plural).
What does J23 mean by what he says?
What he says in that sentence has to be harmonized with his other statement in the same section: "Christ Himself ... immolates Himself each day for all of us." That's where we encounter the repetition of the sacrifice. Most people don't have the word "immolate" in their daily vocabulary. Here's a standard definition:
IM'MOLATE, v.t. [L. immolo, to sacrifice; in and mola,meal sprinkled with salt, which was thrown on the head of the victim.](Webster's 1828 Dictionary)
1. To sacrifice; to kill, as a victim offered in sacrifice.
2. To offer in sacrifice.
To immolate means to slay - to kill - as a sacrificial victim. The idea that Christ is sacrificing himself daily is basis for viewing each mass as a sacrifice. The result is that Christ is immolated not once on Calvary but innumerable times.
In what sense then is there one sacrifice in Catholicism? You will be hard-pressed for a detailed explanation from the Roman pontiff. One way of looking it at is as there being only one category of sacrifice: there is no sacrifice of sheep, goats, or oxen, only of Christ.
Another way of looking at it is as a repetition of Christ's sacrifice. While this terminology is currently disfavored in Roman Catholic theology, we find it expressed plainly even in the fairly recent writings:
28 Just as Moses with the blood of calves had sanctified the Old Testament, (Cf. Ex 24,8) so also Christ Our Lord, through the institution of the Mystery of the Eucharist, with His own Blood sanctified the New Testament, whose Mediator He is. For, as the Evangelists narrate, at the Last Supper "He took bread, and blessed and broke it, and gave it to them, saying: "This is My Body, given for you; do this for a commemoration of Me. And so with the cup, when supper was ended. This cup, he said, is the New Testament, in My Blood which is to be shed for you.'" (Lc 22,19-20; cf. Mt 26,26-28 Mc 14,22-24) And by bidding the Apostles to do this in memory of Him, He made clear His will that the same sacrifice be forever repeated.(Mysterium Fidei, Paul VI, 3 September 1965)
However, in "ecumenical" materials we find explicit disclaimer of this sort of claim:
In other words, we are sacramentally united with Christ, as his body, in the great single act of his sacrifice, by which he entered into glory. There can never be any repetition of that act; it happened once and for all (Hebrews 10:10).- The Grace Given You in Christ, (connected to dialog with World Methodist Council), Section 131, 2006
And previously in the same dialog:
Roman Catholics can happily accept all these senses of the term, but they are also accustomed to speak of the sacrifice of the Mass as something which the church offers in all ages of her history. They see the eucharist not as another sacrifice adding something to Christ’s once-for-all sacrifice, nor as a repetition of it, but as making present in a sacramental way the same sacrifice.- The Dublin Report (connected to dialog with World Methodist Council), Section 66, 1976
We agree that the Eucharist is the memorial (anamnesis) of the crucified and risen Christ, of the entire work of reconciliation God has accomplished in him. By memorial, Anglicans and Catholics both intend not merely a calling to mind of what God has done in the past but an effectual sacramental proclamation, which through the action of the Holy Spirit makes present what has been accomplished and promised once-and-for-all. In this sense, then, there is only one historical, unrepeatable sacrifice, offered once for all by Christ and accepted once for all by the Father, which cannot be repeated or added to. The eucharistic memorial, however, makes present this once-and-for-all sacrifice of Christ. It is therefore possible to say that “the Eucharist is a sacrifice in the sacramental sense, provided that it is clear that this is not a repetition of the historical sacrifice.” “In the Eucharistic Prayer, the Church continues to make a perpetual memorial of Christ’s death, and his members, united with God and one another, give thanks for all his mercies, entreat the benefits of his passion on behalf of the whole Church, participate in these benefits, and enter into the movement of his self-offering.” The action of the Church in the eucharistic celebration “adds nothing to the efficacy of Christ’s sacrifice on the cross” but is rather a fruit of that sacrifice. In the eucharistic celebration Christ’s one sacrifice is made present for us.- Growing Together in Unity and Mission (connected with dialog with Anglicans), Chapter 5, Section 40
Yet we see much the same thought even after the dialog, although the word choice has changed so that we see it expressed as a "renewal":
He also instituted the priesthood as a sacrament of the New Covenant, so that the one sacrifice he offered to the Father in a bloody manner might be continually renewed in the Church in an unbloody manner, under the appearances of bread and wine.- John Paul II, Homily of 1 April 1999, Section 2
and as a "perpetuation":
This union of the Mother and the Son in the work of redemption(57) reaches its climax on Calvary, where Christ "offered himself as the perfect sacrifice to God" (Heb. 9:14) and where Mary stood by the cross (cf. Jn 19:25), "suffering grievously with her only-begotten Son. There she united herself with a maternal heart to His sacrifice, and lovingly consented to the immolation of this victim which she herself had brought forth"(58) and also was offering to the eternal Father."(59) To perpetuate down the centuries the Sacrifice of the Cross, the divine Savior instituted the Eucharistic sacrifice, the memorial of His death and resurrection, and entrusted it to His spouse the Church,(60) which, especially on Sundays, calls the faithful together to celebrate the Passover of the Lord until He comes again.(61) This the Church does in union with the saints in heaven and in particular with the Blessed Virgin,(62) whose burning charity and unshakable faith she imitates.- Marialis Cultis, Paul VI, 1974
The Eucharist is the very sacrifice of the Body and Blood of the Lord Jesus which he instituted to perpetuate the sacrifice of the cross throughout the ages until his return in glory.- Compendium of the Catechism of the Catholic Church, Question 271
The preferred method of expression currently is that the Eucharist "makes present" the one sacrifice:
The Eucharist is a memorial in the sense that it makes present and actual the sacrifice which Christ offered to the Father on the cross, once and for all on behalf of mankind. The sacrificial character of the Holy Eucharist is manifested in the very words of institution, “This is my Body which is given for you” and “This cup is the New Covenant in my Blood that will be shed for you” (Luke 22:19-20). The sacrifice of the cross and the sacrifice of the Eucharist are one and the same sacrifice. The priest and the victim are the same; only the manner of offering is different: in a bloody manner on the cross, in an unbloody manner in the Eucharist.- Compendium of the Catechism of the Catholic Church, Question 280
The Mass makes present the sacrifice of the Cross; it does not add to that sacrifice nor does it multiply it. What is repeated is its memorial celebration, its “commemorative representation” (memorialis demonstratio), which makes Christ's one, definitive redemptive sacrifice always present in time. The sacrificial nature of the Eucharistic mystery cannot therefore be understood as something separate, independent of the Cross or only indirectly referring to the sacrifice of Calvary.- John Paul II, Ecclesia de Eucharistia, Chapter 1, Section 12 (17 April 2003)
But I have digressed. Consider the absurdity of the matter. Why would you need a memorial for something that is there? No one visits the memorial of a battle during the battle, and everyone recognizes that recreations or memorial representations of battles are not the real thing but a symbol or sign of the thing.
The reason for this bizarre claim that the sacrament is both the reality and a memorial is caused by Roman unwillingness to acknowledge her mistake in viewing each mass as a literal sacrifice of Christ. That view is wrong and inconsistent with there being only one sacrifice. The Scriptures plainly teach the "one sacrifice" view and Rome ought simply to submit to that, instead of trying to hold onto both views at the same time.