Last week, Pope Francis gave a short talk to a gathering of Italian liturgists. (The Vatican website has posted the text of the speech in Italian only, so far.)
(Three excellent takes on this talk are Fr. Hunwicke's, Fr. Zuhlsdorf's, and Dr. Ed Peter's.)
Much of what the Holy Father said is unexceptional, even inspiring. He began with a brief summary of the process of liturgical reform, noting such luminaries as Pius X, Pius XII and the 1947 encyclical Mediator Dei (a marvelous and inspiring work), and the sacred consitution on the liturgy of the Second Vatican Council, Sacrosanctum Concilium. And he concluded with some thoughts about the "vivifying" character of the liturgy, particularly of the Holy Mass, noting especially (1) our Eucharistic participation in Christ's life-giving victory over sin and death, (2) the unity of the Church which flows from the sacraments (uniting peoples with peoples, and laity with clergy, and whole Church with Christ her Head), and (3) the importance of "mystagogical catechesis" (as of the Fathers, he noted) for revealing and sustaining our personal and corporate relationship with Christ. All this was quite good.
And yet, as he too often does, Pope Francis managed to say something that sounded immensely important, but with a great degree of ambiguity and confusion.
Following his summary of Sacrosanctum Concilium, he talked about the implementation of the liturgical reforms by Pope Paul VI. He said, "It's not enough to reform the books, in order to renew the (liturgical) mentality." He twice insisted on the identity (!!) of the enacted reforms with the intentions of the Council Fathers and text of SC. And he stated that "...we can affirm with security and magisterial authority that the litugical reform is irreversible."
I agree that the liturgical mentality in the Church in much of the 19th and 20th centuries needed to be renewed. Under the cultural pressures of the Revolution(s) and the Enlightenment, the mentality of the Church became constricted, in several areas. Low Mass became the norm, rather than High Mass; minor orders fell into disuse in nearly all parishes; Gregorian chant became ossified, and congregations were little able to sing their parts; and so on. Against these trends, the Liturgical Movement was attempting precisely to renew the Church's culture of worship, starting with the refounding of the great abbey of Solemnes after its destruction during the French Revolution, and the renewal of its monastic liturgy. It slowly gained momentum before Vatican II.
It's impossible, however, not to notice that much (not all, certainly, but much) of the implementation of the postconciliar reforms changed the nature and the direction of that Movement. It's also impossible not to notice that, on several significant points, the implementation of the reforms did or attempted things not called for in SC, and also did or attempted things contrary to what SC called for. The result has not been a renewal of a vital litugical mentality, but the further erosion of what vitality remains. Where immediately before the Council, liturgy was very often done hastily, carelessly (of the Latin, of the reverence expected, etc), and therefore sloppily, immediately after the implementation of reforms, liturgy came to be done "experimentally," iconclastically, "self-referentially" (ironically, one of Pope Francis's more significant criticisms of the modern Church), and still more sloppily. The "Low Mass" mentality that prevailed was not renewed, it was cemented, and the spirit of modern lawlessness was added to it.
Pope Benedict XVI understood these trends profoundly. He grasped, and taught repeatedly, both that the practical implementation of the Council's vision of liturgical renewal had failed on several points, and needed to be very carefully reviewed, reconsidered, and corrected (this is often dubbed "the reform of the reform"), and that the Church will never be able to evangelize effectively in the modern world, with banal liturgy (!!!). On the first point, he led by example, and also gave the Church the gift of Summorum Pontificum, not out of a sense of nostalgia, but as a "restart" of the intended renewal. If we can remember the right way to undertake the liturgy in the "extraordinary form" -- that is, reverently, in union with Tradition and with the angelic, Heavenly liturgy, and in a manner that elevates hearts and minds to God -- then we can apply that to the "ordinary form," and find or develop the intended renewal there. On the second point, he preached loudly and incessantly about worldly banality as the prototypical illness of modernity, and that the medicine to cure it is true, deep, personal encounter with Christ, divine Love personified - best found in a vital, authentic, devoutly Catholic worship.
It is, therefore, very difficult to understand quite what the Holy Father means by asserting "irreversibility." It seems that the statement must either be a tautology, or else factually false.
Like so much else in the contemporary Church, that falsity is directly the fruit of the poor practical implementation of the desired reforms of SC. Fortunately, a good part of that needed "reform of the reform" has already begun, at least in some places; for example, a return to Gregorian chant (sometimes with classical Latin pieces, but even more so with new, vernacular plain-chant); a rejection of ugly, polyester vestments and burlap banners, and a retrieval of more beautiful and fitting vestments, church adornment, etc; a rejection of side-lining Christ in the tabernacle, and a return to "front and center" placement; the related re-emergence of Adoration and similar devotions; and so on. None of this means a rejection of Vatican II's liturgical reform and renewal. It _is_ the renewal. And, God willing, it will indeed prove "irreversible."