If the Old Mass was used by Popes since Gregory I, if Quo Primum of Pius V forbade and condemned changes, if Pius XII in Mediator Dei forbade innovations like the altar facing the people and the vernacular, how can traditional Catholics be disobedient for wanting the Mass of the ages?

They are not, as I will explain.

First, many features of the Mass do not enjoy the longevity you mention. Liturgical studies encouraged by the Popes since the 1800s have shown that while the core elements of the Roman Mass have not changed many of the lesser elements have. The most authoritative account of this history is Fr. Josef Jungmann's two volumes The Mass of the Roman Rite. Up until Trent the Mass could differ between regions and dioceses,  as local adaptations were made to a basic Latin Rite. Rome did not, and practically could not, exercise so firmly her supreme authority over the liturgy. 

The Reformation changed that, and the Holy See reserved authority to herself. The question is not whether the Church was or is bound to the liturgical form promulgated for universal usage in the Roman Rite by Pope St. Pius V through Quo Primum, she is not, but who has authority to make changes. This is why Pope Pius XII, Vatican II and the 1983 Code of Canon Law all state that any changes in the Liturgy must come from the Holy See. The Popes, like Pius V in Quo Primum and Pius XII in Mediator Dei, decry and forbid innovations, changes by those without authority. This safeguards the essential forms, and thus the validity, of the sacraments. The Supreme authority in the Church, a Pope or a Council in union with the Pope, always has the authority to make changes to ecclesiastical discipline, such as the liturgical forms that cloak the essential matter and form of a sacrament. Pius XII made changes, John XXIII made changes, Vatican II proposed changes, and Pope Paul VI and Pope John Paul II have made changes. All have understood that Popes do not bind other Popes or Councils in such matters, otherwise the Supreme authority would not be Supreme.

As for the altar and the vernacular, it is up to the Supreme Magisterium to determine when, and where, and for whom, they are opportune. Both options of altar and language have been used in the Church. These are prudential disciplinary matters not matters of faith, which are protected by the charism of infallibility. However, even in such disciplinary matters the Church cannot err so as to undermine the validity of the sacraments, otherwise Christ' promise to be with His Church would fail.  They are prudential judgments about which popes and Catholics may be of different opinions. Popes and Catholics are not bound to respect your and my opinion on the matter. Catholics are bound to respect that of Popes, however, as a practical matter of ecclesiastical communion. That is what the doctrine of Papal Primacy teaches. 

...all the faithful of Christ must believe "that the Apostolic See and the Roman Pontiff hold primacy over the whole world, and that the Pontiff of Rome himself is the successor of the blessed Peter, the chief of the apostles, and is the true vicar of Christ and head of the whole Church and faith, and teacher  of all Christians; and that to him was handed down in blessed Peter, by our Lord Jesus Christ, full power to feed, rule, and guide the universal Church, just as is also contained in the records of the ecumenical Councils and in the sacred canons.

... the faithful of whatever rite and dignity, both as separate individuals and all together, are bound by a duty of hierarchical submission and true obedience, not only in things pertaining to faith and morals, but also in those which pertain to the discipline and government of the Church spread over the whole world, so that the Church of Christ, protected not only by the Roman Pontiff, but by the unity of communion as well as of the profession of the same faith is one flock under the one highest shepherd. This is the doctrine of Catholic truth from which no one can deviate and keep his faith and salvation..." [Dogmatic Constitution on the Church, Vatican Council I, 1870]

All Catholics should respect the teaching and authority of the Church – whether manifested through a Council or a Pope. As for preferring the traditional rites, since the Holy See has shown its solicitude for traditional Catholics it can hardly be a matter of disobedience to prefer the Tridentine Mass. It would be theologically untenable to argue that in and of itself there could be any grounds for claiming so. Disobedience is a matter of a person's will knowingly rejecting lawful authority. Where that is not present there is no disobedience. In matters of the liturgy, the Holy See is that authority, and its willingness to satisfy the aspirations of traditional Catholics is clear.

Answered by Colin B. Donovan, STL

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