...The first use of the phrase 'active participation' as a desideratum for lay involvement in the liturgy was in the Italian version of St. Pius X's motu proprio Tra le Sollicitudini in 1903; it did not appear in the official Latin text.

The first occurrence of the idea in a magisterial document seems to be in Pius XI's Apostolic Constitution Divini Cultus (1928), where he stated that “In order that the faithful may more actively participate in divine worship, let them be made once more to sing the Gregorian Chant, so far as it belongs to them to take part in it.” This understanding of active participation was spelled out under Pius XII...

...The magisterial teaching on the importance of the active participation of the laity can be seen from these statements to be part of a larger project; that of making High Mass or at least a sung mass, rather than Low Mass, the norm for Sunday worship in Catholic parishes. This goal is itself implied by the teaching on the necessity of the use of Gregorian chant in mass as the norm, which itself requires a sung mass of some kind. It meant a radical departure from the common practice of the laity attending a Low Mass on Sunday and saying the rosary or other devotions during the mass....

...we need to distinguish between the participation of the laity in the liturgy as a relative notion – the proportion of the activity in the mass undertaken by the laity as opposed to the clergy in the liturgy – and participation as an absolute notion; the amount of activity undertaken by the laity in the liturgy in absolute terms. Participation here is not understood as including all spiritual activity undertaken by the laity in connection with the liturgy, but in the obvious sense of externally observable activity by the laity that forms part of the liturgical celebration; baldly, what is written in the liturgical books and done by the laity. When this distinction is made, it can be seen that the traditional mass permits much more participation by the laity in absolute terms. The content of the lay participation that can be undertaken by the whole congregation is what is found in the Kyriale Romanum. Learning to sing this content properly and singing it regularly every Sunday is a much more rich, complex, and difficult task than anything available to the laity in the Novus Ordo....

...Those societies which have acknowledged the true God or believed in false gods have been convinced that worship is among the most serious and important activities of individuals, families and communities, because it is decisive for the fates of the worshippers in this world and the next. They have accordingly devoted an important part of their energies to worship. They have developed styles of architecture, and constructed elaborate buildings in these styles – Greek architecture is one style among many that was developed primarily for the construction of temples. They have developed music; both polyphony and musical notation were developed by the Catholic Church for religious purposes. They have developed and used elaborate and rich garments for the main functionaries in religious worship, and – most significantly for our purposes – they have devised complex and precise rituals that follow pre-established rules. The fundamental idea behind all this effort is that an activity of supreme importance has to have great thought, care and resources devoted to it, resulting in a complex and elaborate structure that uses all the highest resources available to a human culture. This result is found in the most disparate societies – ancient Egypt, China, India, the Aztecs, Babylon, the kingdom of Judah in the Old Testament, the Christian Church – despite the vast differences between the entities they worshipped, simply because they share this basic idea about the supreme importance of worship. A special priestly class has been necessary in all these societies for the single reason that the complexity of worship makes its direction a full-time job, which only those with long specialised training are capable of undertaking. The development of special liturgical languages is a natural result of this process. The ritual of worship has a sacred character, which means that it is preserved in its original linguistic form when the spoken language changes. Again this development of a liturgical language – Latin, Old Church Slavonic, Geez, Sanskrit, Pali – is common to the most disparate forms of religious belief....