Here is what
Pope John Paul II explained is meant by “full, conscious, and active participation” in the liturgy:
The sharing of all the baptized in the one priesthood of Jesus Christ is the key to understanding the Council’s call for full, conscious and active participation in the liturgy.
Full participation certainly means that
every member of the community has a part to play in the liturgy; and in this respect a great deal has been achieved in parishes and communities across your land. But full participation
does not mean that everyone does everything, since this would lead to a clericalizing of the laity and a laicizing of the priesthood; and this was not what the Council had in mind. …]
Active participation certainly means that,
in gesture, word, song and service, all the members of the community take part in an act of worship, which is anything but inert or passive. Yet active participation
does not preclude the active passivity of silence, stillness and listening: indeed, it demands it. …]
Conscious participation calls for the entire community to be
properly instructed in the mysteries of the liturgy, lest the experience of worship degenerate into a form of ritualism. But it
does not mean a constant attempt within the liturgy itself to make the implicit explicit, since this often leads to a verbosity and informality which are alien to the Roman Rite and end by trivializing the act of worship.
Nor does it mean the suppression of all subconscious experience, which is vital in a liturgy which thrives on symbols that speak to the subconscious just as they speak to the conscious. …]
You can read his full remarks at the link above; I’ve excised a lot of content.
We can go further back and look at the description of participation in the liturgy found in the 1967 (post-Vatican II) Instruction
Musicam Sacram which, despite its name, deals with more than just “sacred music”.
The faithful fulfil their liturgical role by making that full, conscious and active participation which is demanded by the nature of the Liturgy itself and which is, by reason of baptism, the right and duty of the Christian people. This participation
(a) Should be
above all internal, in the sense that by it the faithful join their mind to what they pronounce or hear, and cooperate with heavenly grace,
(b)
Must be, on the other hand, external also, that is, such as to show the internal participation by gestures and bodily attitudes, by the acclamations, responses and singing.
We could look even further back, to the 1958 (pre-Vatican II) Instruction
De Musica Sacra which also deals with more than just “sacred music”:
By its very nature, the Mass requires that all present take part in it, each having a particular function.
a)
Interior participation is the most important; this consists in paying devout attention, and in lifting up the heart to God in prayer. In this way the faithful “are intimately joined with their High Priest…and together with Him, and through Him offer (the Sacrifice), making themselves one with Him”.
b) The participation of the congregation becomes
more complete, however, when, in addition to this interior disposition, exterior participation is manifested by external acts, such as bodily position (kneeling, standing, sitting), ceremonial signs, and especially responses, prayers, and singing.
The Supreme Pontiff Pius XII, in his encyclical on the sacred liturgy, Mediator Dei, recommended this form of participation: “Those who are working for the exterior participation of the congregation in the sacred ceremonies are to be warmly commended. This can be accomplished in more than one way. The congregation may answer the words of the priest, as prescribed by the rubrics, or sing hymns appropriate to the different parts of the Mass, or do both. Also, at solemn ceremonies, they may alternate in singing the liturgical chant”.
When the papal documents treat of “active participation” they are speaking of this general participation, of which the outstanding example is the priest, and his ministers who serve at the altar with the proper interior dispositions, and carefully observe the rubrics, and ceremonies.
c)
Active participation is perfect when “sacramental” participation is included. In this way “the people receive the Holy Eucharist not only by spiritual desire, but also sacramentally, and thus obtain greater benefit from this most holy Sacrifice”.
d) Since
adequate instruction is necessary before the faithful can intelligently, and actively participate in the mass, it will help to note here a very wise law enacted by the Council of Trent: “This holy Council orders that pastors, and all those who are entrusted with the care of souls shall frequently give a commentary on one of the texts used at Mass, either personally or through others, and, in addition, explain some aspect of the mystery of this holy Sacrifice; this should be done especially on Sundays, and feast days in the sermon which follows the Gospel” (or “when the people are being instructed in the catechism)”.
