Mental Prayer is Objectively Superior to Vocal
The most important critique of the liturgical reforms under Ven. Pius XII and St. Paul VI is rarely heard: the reformers denied that mental prayer is objectively superior to vocal prayer. Before the New Mass, each faithful soul participated in the Holy Sacrifice in different ways—some prayed vocally, others assisted in the choir or at the altar, but many others prayed mentally. The creators of the New Mass believed that by forcing everyone’s mental prayer into one large, vocal prayer assembly, they would be “liberating” the faithful from being “passive spectators” to enter into some superior form of spirituality. This is the so-called “active participation,” a term which has a long, multifaceted history. This is shown from Sacrosanctum Concilium at Vatican II, the only draft document (written by Bugnini) not thrown out of the Council by the reformers:
In the restoration and promotion of the sacred liturgy, this full and active participation by all the people is the aim to be considered before all else; for it is the primary and indispensable source from which the faithful are to derive the true Christian spirit (14).
Thus it was supposed by the reformers that our fathers, who bled and died for the faith, were deprived of the “true Christian spirit” because they were (mostly) silent before a nebulous, Latin liturgy. But this preference for active and public vocal prayer over private mental prayer is a spiritual error. Would the reformers have taken issue with St. Teresa of Avila in ecstasy at Holy Mass since she wasn’t singing with the congregation?
On the contrary, the spiritual writers say that mental prayer is objectively superior to vocal prayer. The Roman Catechism declares in the section on Mental Prayer:
This spiritual manner of praying does not exclude the use of vocal prayer. Nevertheless, that prayer which is the vehement outpouring of the soul, deservedly holds the first place; and although not uttered with the lips, it is heard by God to whom the secrets of hearts are open (Part 4 Introduction).
After discussing Vocal prayer, Garrigou-Lagrange writes
But we feel the need of a more intimate prayer, in which our soul, more profoundly recollected, comes into contact with the Blessed Trinity dwelling in us [which] can make us penetrate deeply and taste the mysteries of salvation: those of the redeeming Incarnation, of the Sacrifice of the Mass, of eternal life toward which we are traveling…This more intimate prayer is mental prayer.
Since prayer is defined as the lifting of the mind and heart to God, mental prayer is on an objective level above vocal prayer because it more closely approximates the Beatific Vision. Mental prayer is the second level in the nine levels of prayer.
The Subjective Nature of Private Devotion
But while it is true that mental prayer is superior on the objective level, it may not always be superior on the subjective level. Vocal prayer, moreover, helps keep our wondering minds attentive. Commenting on public and private prayer, Garrigou-Lagrange writes
From mental prayer the Office receives the habit of recollection and the spirit of prayer. On the other hand, mental prayer finds in liturgical prayer an abundant source of contemplation and an objective rule against individual illusions.
This means that each individual soul must use whatever means he needs at Holy Mass in order to hear Mass devoutly. Again Garrigou-Lagrange:
We may use different ways to assist well at Mass, with faith, confidence, true piety, and love. We can be attentive to the liturgical prayers, which are generally beautiful and full of unction, elevation, and simplicity. We can also recall the passion and death of the Savior, of which the Mass is the memorial, and think of ourselves as standing at the foot of the cross with Mary, John, and the holy women. Again, we can apply ourselves to rendering to God, in union with Christ, the four duties that are the ends of the sacrifice: adoration, reparation, petition, and thanksgiving. Provided we pray, even while piously saying the Rosary, we assist fruitfully at Mass. We may, like St. Jane de Chantal and many saints, with great profit continue our mental prayer during the Mass, especially if we are inclined to a pure and intense love, somewhat like St. John resting on the breast of Jesus at the Last Supper 
Thus the Holy Mass is indeed the moment for the “people of God” to offer the sacrifice of Holy Mass together to Almighty God. And yet, it is a mistake of the reformers to think that everyone must participate externally in the same way or to denigrate the pious practices of many faithful. These errors of the reformers were opposed by Ven. Pius XII when he declared in 1947:
So varied and diverse are men’s talents and characters that it is impossible for all to be moved and attracted to the same extent by community prayers, hymns and liturgical services. Moreover, the needs and inclinations of all are not the same, nor are they always constant in the same individual. Who, then, would say, on account of such a prejudice, that all these Christians cannot participate in the Mass nor share its fruits? On the contrary, they can adopt some other method which proves easier for certain people; for instance, they can lovingly meditate on the mysteries of Jesus Christ or perform other exercises of piety or recite prayers which, though they differ from the sacred rites, are still essentially in harmony with them (Mediator Dei, 108)
Unfortunately, only a few years later, Pius XII would approve his radical change to Holy Week, which allowed Bugini to take his first shots against the cherished devotions of the faithful. This reform reoriented the liturgy to disallow or suppress the various practices to which that the faithful were accustomed (for example, the 40 hours devotion). The reformers called the Pius Holy Week reform the “first battering ram that pierced through a hitherto static liturgy.” In their mind, they were liberating the faithful from their own prayers into the higher form of “active participation.” In reality, they were introducing a spiritual error which would eventually erupt in the later 60s and 70s with the promulgation of the New Mass. In one of the many contradictions of the conciliar revolution, the reformers forced everyone to abandon their prayers and pray in a way they never asked for, all in the name of being “pastoral.”
Timothy S. Flanders
 Three Ages of the Interior Life, Part I, chapter 35. See also Jordan Aumann Spiritual Theology, pp. 316ff
 Ibid., Ch. 34