"I am worried by the Blessed Virgin's messages to Lucy of Fatima. This persistence of Mary about the dangers which menace the Church is a divine warning against the suicide of altering the Faith in her liturgy..."
...Puis XII Devant L'Histoire
"If anyone says that the received and approved rites of the Catholic Church customarily used in the solemn administration of the sacraments may be despised, or may be freely omitted by the ministers without sin, or may be changed into other new rites by any church pastor whomsoever, let him be anathema."
...Council of Trent, Sess. VII, Can. XIII
Pope Paul III, 3 March 1547 (D.S. 1613)
"... 'recalling it (the liturgy) to greater simplicity of rites, by expressing it in the vernacular language or by uttering it in a loud voice' as if the present order of the liturgy received and approved by the Church, had emanated in some part from the forgetfulness of the principles by which it should be regulated ... (is) rash, offensive to pious ears, insulting to the Church, favourable to the charges of heretics".
...Auctorem Fidei 
Pope Pius VI, 28 August 1794 (D.S. 2633)
"Suppose, dear friend, that Communism [one of "the errors of Russia" mentioned in the Message of Fatima] was only the most visible of the instruments of subversion to be used against the Church and the traditions of Divine Revelation...
"I am worried by the Blessed Virgin's messages to Lucy of Fatima. This persistence of Mary about the dangers which menace the Church is a divine warning against the suicide of altering the Faith, in her liturgy, her theology and her soul. ...
"I hear all around me innovators who wish to dismantle the Sacred Chapel, destroy the universal flame of the Church, reject her ornaments and make her feel remorse for her historical past.
"A day will come when the civilized world will deny its God, when the Church will doubt as Peter doubted. She will be tempted to believe that man has become God. In our churches, Christians will search in vain for the red lamp where God awaits them, like Mary Magdalene weeping before the empty tomb, they will ask, "Where have they taken Him?" (emphasis added)
... Pope Pius XII
Quoted in the book Pius XII Devant L'Histoire, pp. 52-53 (by Msgr. Georges Roche)