Many thanks to the reader who posted this in the comments section of an older post. It is something that I had not seen before:
The text of Paul VI’s General Audience talk right before the new rite of the Mass was introduced on the First Sunday of Advent, 1969:

Our Dear Sons and Daughters:
1. We ask you to turn your minds once more to the liturgical innovation of the new rite of the Mass. This new rite will be introduced into our celebration of the holy Sacrifice starting from Sunday next which is the first of Advent, November 30 [in Italy].
2. A new rite of the Mass: a change in a venerable tradition that has gone on for centuries. This is something that affects our hereditary religious patrimony, which seemed to enjoy the privilege of being untouchable and settled. It seemed to bring the prayer of our forefathers and our saints to our lips and to give us the comfort of feeling faithful to our spiritual past, which we kept alive to pass it on to the generations ahead.
3. It is at such a moment as this that we get a better understanding of the value of historical tradition and the communion of the saints. This change will affect the ceremonies of the Mass. We shall become aware, perhaps with some feeling of annoyance, that the ceremonies at the altar are no longer being carried out with the same words and gestures to which we were accustomed—perhaps so much accustomed that we no longer took any notice of them. This change also touches the faithful. It is intended to interest each one of those present, to draw them out of their customary personal devotions or their usual torpor.
4. We must prepare for this many-sided inconvenience. It is the kind of upset caused by every novelty that breaks in on our habits. We shall notice that pious persons are disturbed most, because they have their own respectable way of hearing Mass, and they will feel shaken out of their usual thoughts and obliged to follow those of others. Even priests may feel some annoyance in this respect.
5. So what is to be done on this special and historical occasion? First of all, we must prepare ourselves. This novelty is no small thing. We should not let ourselves be surprised by the nature, or even the nuisance, of its exterior forms. As intelligent persons and conscientious faithful we should find out as much as we can about this innovation. It will not be hard to do so, because of the many fine efforts being made by the Church and by publishers. As We said on another occasion, we shall do well to take into account the motives for this grave change. The first is obedience to the Council. That obedience now implies obedience to the Bishops, who interpret the Council’s prescription and put them into practice.
6. This first reason is not simply canonical—relating to an external precept. It is connected with the charism of the liturgical act. In other words, it is linked with the power and efficacy of the Church’s prayer, the most authoritative utterance of which comes from the Bishop. This is also true of priests, who help the Bishop in his ministry, and like him act in persona Christi (cf. St. Ign., ad Eph. I, V). It is Christ’s will, it is the breath of the Holy Spirit which calls the Church to make this change. A prophetic moment is occurring in the mystical body of Christ, which is the Church. This moment is shaking the Church, arousing it, obliging it to renew the mysterious art of its prayer.
7. The other reason for the reform is this renewal of prayer. It is aimed at associating the assembly of the faithful more closely and more effectively with the official rite, that of the Word and that of the Eucharistic Sacrifice, that constitutes the Mass. For the faithful are also invested with the “royal priesthood”; that is, they are qualified to have supernatural conversation with God.
8. It is here that the greatest newness is going to be noticed, the newness of language. No longer Latin, but the spoken language will be the principal language of the Mass. The introduction of the vernacular will certainly be a great sacrifice for those who know the beauty, the power and the expressive sacrality of Latin. We are parting with the speech of the Christian centuries; we are becoming like profane intruders in the literary preserve of sacred utterance. We will lose a great part of that stupendous and incomparable artistic and spiritual thing, the Gregorian chant.
9. We have reason indeed for regret, reason almost for bewilderment. What can we put in the place of that language of the angels? We are giving up something of priceless worth. But why? What is more precious than these loftiest of our Church’s values?
10. The answer will seem banal, prosaic. Yet it is a good answer, because it is human, because it is apostolic.

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