Fr. Kramer: Quo Primum Is Not Disciplinary
As is the case with Cum ex apostolatus officio, Quo Primum was published by St. Pius V not as a mere disciplinary decree, but as a definitive and irrevocable application of divine law. Adherence to the traditional rites is an article of faith -- it is de fide.
The Council of Constance, Sess. 39, infallibly teaches that the pope is bound to the traditional rites, and adherence to them is prescribed in the Profession of Faith (Vatican Council I). Hence, since the divine law binds the Church to the traditional rites established by custom and "received and approved" by the Church, perpetual adherence to the rite handed down by the Roman Church pertains to divine law. Therefore once the Roman Rite became the customary rite throughout the Roman Patriarchate, it thereby became the "received and approved" rite of that patriarchate; and as such became binding on the churches of that Patriarchate by divine law. Therefore, St. Pius V with full knowledge of the applicability of divine law to the matter of perpetual adherence to the traditional rite solemnly pronounced by Apostolic Authority, "We statute, declare, and decree, that this present document can never be revoked or modified, but remains forever in force". He solemnly declared Quo Primun to be irrevocable, unalterable, and forever valid and binding. All the popes up to Montini knew full well that they were bouund by Quo Primun as a matter of divine law. Then the Milan Modernist Mafia under Capomafia Montini decided behind closed doors that Quo Primun was only "disciplinary", and then they foisted their schismatic "new rite" (Montini's words 19/11/1969) on all the churches of the Latin Patriarchate in 1970 -- unleashing the wrath of God and the holy Apostles Peter & Paul.