This was promulgated last month, addressing questions like this one:
If a Priest who has been granted the use of the Missale Romanum of 1962 does not recognize the validity and legitimacy of concelebration – refusing to concelebrate, in particular, at the Chrism Mass – can he continue to benefit from this concession?
The answer is:
The Chrism Mass has been an important expression of diocesan/clerical unity for at least three generations. Bishops take this kind of thing quite seriously. When priests opt out of the team, ordinaries get unhappy.
Rome doesn’t want the unhappy on the other side to make too much fuss. Pope Francis would recommend accompaniment in this instance. His two predecessors would counsel catechesis:
However, before revoking the concession to use the Missale Romanum of 1962, the Bishop should take care to establish a fraternal dialogue with the Priest, to ascertain that this attitude does not exclude the validity and legitimacy of the liturgical reform, the teaching of the Second Vatican Council and the Magisterium of the Supreme Pontiffs, and to accompany him towards an understanding of the value of concelebration, particularly at the Chrism Mass.
These questions and answers are accompanied by an Explanatory note.
Art. 3 § 1 of the Motu Proprio Traditionis custodes requires the diocesan Bishop to ascertain that the groups requesting to celebrate with the Missale Romanum of 1962 “do not deny the validity and the legitimacy of the liturgical reform, dictated by Vatican Council II and the Magisterium of the Supreme Pontiffs”.
St Paul forcefully reminds the community of Corinth to live in unity as a necessary condition to be able to participate at the Eucharistic table (cf. 1 Corinthians 11,17-34).
These two aspects seem crucial. Perhaps it burns that a passage used often to deny the sacraments to sinners is applied to clergy who decline to observe any sort of Mass in the modern Roman Rite.
In the Letter sent to the Bishops of the whole world to accompany the text of the Motu Proprio Traditionis custodes, the Holy Father says: “Because ‘liturgical celebrations are not private actions, but celebrations of the Church, which is the sacrament of unity’ (cf. Sacrosanctum Concilium 26), they must be carried out in communion with the Church. Vatican Council II, while it reaffirmed the external bonds of incorporation in the Church — the profession of faith, the sacraments, of communion — affirmed with St. Augustine that to remain in the Church not only ‘with the body’ but also ‘with the heart’ is a condition for salvation (cf. Lumen Gentium 14)”.
I would add that not only is the celebration of liturgy not private, it is also not personal. That is, subject to the whims and desires of individuals. Refusing to join with one’s brother clergy on important days is a fairly grave and audacious step to take:
The explicit refusal not to take part in concelebration, particularly at the Chrism Mass, seems to express a lack of acceptance of the liturgical reform and a lack of ecclesial communion with the Bishop, both of which are necessary requirements in order to benefit from the concession to celebrate with the Missale Romanum of 1962.
It is important to note the reiteration of the need for dialogue between bishop and priest:
However, before revoking the concession to use the Missale Romanum of 1962, the Bishop should offer the Priest the necessary time for a sincere discussion on the deeper motivations that lead him not to recognize the value of concelebration, in particular in the Mass presided over by the Bishop. He should invite him to express, in the eloquent gesture of concelebration, that ecclesial communion which is a necessary condition for being able to participate at the table of the Eucharistic sacrifice.