An excellent article from the New Liturgical Movement.
“Pope Francis’ new motu proprio Traditionis Custodes repeatedly appeals to two objective goods as justifications for the measures it imposes: the unity of the Church, and the preservation in Church practice of the Second Vatican Council’s reforms. A number of commentators have already addressed the first issue, with more opinions coming out by the hour. I am concerned only with the second.
“Traditionis Custodes imposes an immediate return to the liturgical climate that existed before Benedict XVI’s 2007 motu proprio Summorum Pontificum. It states that this return is urgently necessary to preserve the heritage of Vatican II. By inescapable implication, to make such an assertion is to state that the status quo ante prior to 2007 was in accord with the Second Council’s reforms. It was not so.
“Indeed, the prevailing condition of Latin liturgy and Latin culture in the Church between the end of the Second Council in 1965 and the 2007 publication of Summorum Pontificum was utterly at odds with the will of St John XXIII, Vatican II’s creator. By extension, it was also contrary to the will of the Council itself, for the Council Fathers never invalidated, altered, or restricted Pope John’s directives on this particular topic, even though they continued in session for more than two years after his death. Logically, then, if the pre-2007 status rerum was not in accord with Vatican II, no one can justify a forcible return to it in the name of the Council.
“Even the most basic outline of modern Church history highlights John XXIII and the Second Vatican Council as gargantuan figures: a portentous reformer and his signature accomplishment. But that is only part of the picture, though it has nearly universally been taken to be the whole. Pope John sought also to be a preserver and a rebuilder of Church tradition, particularly with regard to the use of Latin.
“His authoritative 1962 document Veterum Sapientia  envisioned and required a broad restoration of Latin culture throughout the Universal Church, and provided an arrestingly concrete and detailed plan to make it happen. This document consists of a six-page Constitutio Apostolica – a statement of general goals and principles – followed by twenty-five pages of practical instructions which reach a granular level of detail – even listing the specific authors to be studied year by year over the course of a seven-year compulsory Latin curriculum for seminarians.
“It would be difficult to exaggerate the solemnity with which Pope John signed his Constitution. He did so on the High Altar of St. Peter’s Basilica, on February 22, 1962, the feast of the Chair of Peter, second only to the Keys as a symbol of papal authority. As he signed, that very Chair’s earthly relics loomed behind him, enshrined in Bernini’s famous cathedra, while before him lay a packed basilica, a sea of faces including those of two hundred bishops and forty cardinals. One struggles to imagine what more he could have done to emphasize the importance of the document he was signing: hire arc lights, perhaps, and set them up in the Piazza San Pietro?
“Pope John’s Constitution contained, in its sixth and final page, an order for the immediate writing of regulations to ensure it would be implemented speedily and properly. These regulations, called in Latin the Ordinationes (English “Ordinances” or “Statutes”) were finished and published just two months later by the Sacred Congregation for Seminaries and Universities.  The Ordinationes were slated to come into legal force in every Catholic university and seminary on earth in October of 1963 ; had they done so, we would today be living in an utterly different world. The death of Pope John on June third of that year appears to be the major reason why the Ordinationes were not put into effect on schedule, even though, on the day of his death, the preparations had already been underway for thirteen months – the last eight of those months with the Second Vatican Council in session. 
“It is harder to account for the near-total oblivion to which Veterum Sapientia has been consigned in the decades since Pope John’s death. It was duly published in the Acta Apostolicae Sedis.  Decades later, the Constitution alone was included on the Vatican website’s document archive, in its Latin original, and only one vernacular version, in Spanish. The Ordinationes, by contrast, were virtually impossible to find anywhere online outside the AAS, nor was any full translation into a modern language published until early this year. 
“And yet it is essential to note that no document of the Second Vatican Council, nor any subsequent papal document, has ever abrogated or even modified Veterum Sapientia. If one defines law as valid statute rather than simply what people happen to be doing, then Veterum Sapientia has been the law and policy of the Universal Church since it was signed, and remains so today.
“What, then, did this law and policy require? What would be our situation now if Pope John’s vision had been respected in practice? It is a matter of bitter irony, at this writing, that the primary reason John XXIII advanced for restoring Latin to its place of honor in the Church was for the sake of Her unity, across space and through time. For Latin, he wrote, “does not favor any one nation, but presents itself with equal impartiality to all… while the Church, precisely because it embraces all nations and is destined to endure to the end of time … of its very nature requires a language which is universal, immutable, and non-vernacular.” 
“The elevated language and rhetorical vistas of the Constitution might have tempted cynical Modernists to dismiss it as mere lip-service to a distant cultural ideal. But no one could maintain this opinion for long who went on to read the Ordinationes. They are concrete, remarkably detailed, and equipped with sharp statutory “teeth.” Some sample passages: 
Instructors who are found to be ineffective for whatever reason, and especially those who are hostile to this language [Latin] are to be removed immediately, lest corrosive indulgence or reprehensible neglect compromise their young students’ first instruction, perhaps irreparably. (II, 7)
Latin language studies in high schools for clerics [major seminaries] have this principal goal: that aspirants to Holy Orders should be able to go to the sources of Sacred Tradition understand the documents of the popes and the councils, and likewise the liturgy. The goal is to make [seminarians] able to use this language [Latin] to learn their major academic disciplines, to write Church documents and letters, and to correspond with their brother clergy of other nations. Finally, at the highest levels, the objective is to make them able to take part in the sort of ecclesiastical debates on articles of Catholic faith and discipline which occur in councils and meetings… (II.i.§2)
This curriculum is to last at least seven years, for young people beginning their Latin classes in seminaries. They are to have no fewer than six hours per week in the first five years, and no fewer than five hours weekly in the remaining two. (II.ii.§1.1)
… the other academic disciplines will have to be sequenced and abridged (and some perhaps cut entirely or left for later), so that Our mandate concerning the time to be given to Latin language study may be obeyed in every respect. (II.ii.§2)
Latin language teaching method ought to cause students to acquire the ability to use it. For this reason, the overflowing philological pot-au-feu which makes up nearly the entire menu in schools of the Humanities, especially graduate schools, will have to be thrown out, since it does not give the nourishment one would reasonably expect from such study. (II.iv.§2)
Any textbook used for teaching Latin syntax shall itself be written in Latin. (II.iv.§7)
The academic disciplines to be taught in Latin are: Theoretical Philosophy; General, Dogmatic and Moral Theology; General and Specialized Introduction to Sacred Scripture, and Canon Law. (II. §2)
The professors by whom the major ecclesiastical academic disciplines are to be taught in Latin must 1. Prepare everything carefully in Latin; the Latin must be clear and correct, as the dignity of these disciplines requires. They are not to rely on extempore speaking as a form of discourse. 2. Be selected for this task with an eye not merely to their expertise in their own discipline, even if it be unique; it must also be ascertained that they possess the requisite knowledge of Latin and ability to use it. 3. Be informed of this requirement in a timely way so that they may prepare themselves to meet it; appropriate support shall be provided to them so that they may prepare. 4. Be removed from their positions if they neglect and hold in contempt the requirement given here for using Latin in their teaching, lest by their instruction and example they harm their students. (III. ii. §6).
“An exhaustive study of Pope John’s vision is beyond the scope of these remarks. But these sample passages make it unavoidably clear that the father of the Second Vatican Council firmly intended the post-Conciliar Church to enjoy a robust intellectual and spiritual culture based on Latin and lived through Latin, as it had done through all its prior history. The Mass itself, which went into the Second Council in Latin and came out of it still in Latin, was to have flourished like the Tree of Life in the middle of a lush garden of letters. How different is this vision from the reality in which we live today!
“To what extent the Council Fathers shared the vision of Veterum Sapientia is an investigable question, especially given what actually happened in the years and decades following the Council’s conclusion. It yet remains a matter of fact that neither the Fathers, nor any subsequent synod, nor indeed any of John’s successors ever abridged or abrogated it. Paul VI, John Paul II, and Benedict XVI, in fact, were careful to cite it in initiatives of their own.”
Retrieved July 29, 2021 from New Liturgical Movement: Traditionis Custodes vs. St John XXIII: Guest Article by Dr Nancy Llewellyn
 As a document type, the Apostolic Constitution is ranked either in first or second place for importance, depending on the source. Rankings of papal documents place the Apostolic Constitution between one and five steps above the Motu Proprio in magisterial authority. One place where its text can be accessed is here: https://www.vatican.va/content/john-xxiii/la/apost_constitutions/1962/documents/hf_j-xxiii_apc_19620222_veterum-sapientia.html
 https://www.vatican.va/archive/aas/documents/AAS-54-1962-ocr.pdf, p. 339 et seq. Accessed 22 July 2021.
 Catholic institutions in the southern hemisphere were ordered to begin implementation in the first academic term of 1964, as October 1963 would have fallen at mid-term
 John XXIII convened the Council on October 11, 1962.
 Apostolic Constitution: https://www.vatican.va/archive/aas/documents/AAS-54-1962-ocr.pdf p. 129 et seq. Accessed 22 July 2021.
 https://veterumsapientia.org/resources/; 1) the Acta Apostolicae Sedis (AAS) is the Vatican equivalent of the US Congressional Record, containing a written record of all official papal communications; 2) numerous secular websites of various kinds, providentially, have preserved online the Latin original text of Veterum Sapientia and offer translations into various languages.
 https://www.papalencyclicals.net/john23/j23veterum.htm. Accessed 21 July 2021.
 All passages from https://veterumsapientia.org/wp-content/uploads/VS-Ordinationes-in-English.pdf. Accessed 22 July 2021