The first of eight articles is brief, but one sentence:
Art. 1. The liturgical books promulgated by Saint Paul VI and Saint John Paul II, in conformity with the decrees of Vatican Council II, are the unique expression of the lex orandi of the Roman Rite.
The meaning hinges on one Latin phrase, translated as “the law of prayer.” An ancient saying draws an equivalency to “the law of belief,” suggesting that as we pray, we believe. Maybe there’s a hint of that here, but I would take the article at its word.
Two popes promulgated the liturgical reforms of Vatican II. (Note: while Pope Benedict approved translations through the CDWDS, the actual Rites were completed and updated from their immediate post-conciliar predecessors under Pope John Paul II.)
These liturgical books were a follow-up to Vatican II, endorsing spirit, theology, and intent of the council bishops. There was no hijacking. There was no nefarious agenda. To be sure, some people were alarmed and hurt. Some of that was caused by clumsy implementation. Some was due to theological disagreement. Or a lack of quality.
However these are viewed, Pope Francis is asserting that the law of prayer in the Roman Church is only expressed in the reformed rites. What does that mean? “Unique” is the word given. The implication is that the rites of the post-Vatican II reform are the only way to express the Church’s law of prayer. Where does that leave the Traditional Latin Mass? Likely not on equal footing.
The approved English translation is here.