If I had a counter, this is the fifth explicit reference to “active participation” in the liturgy constitution. While the council acknowledges long-held Catholic teaching about any of the Church’s liturgies being a communal enterprise, it states the preference for incarnation. By that I mean the outward expression of liturgy impacting the sanctification of believers.
It is to be stressed that whenever rites, according to their specific nature, make provision for communal celebration involving the presence and active participation of the faithful, this way of celebrating them is to be preferred, so far as possible, to a celebration that is individual and quasi-private.
This applies with especial force to the celebration of Mass and the administration of the sacraments, even though every Mass has of itself a public and social nature.
It is clear to see the council’s preference for public liturgy and against trends to human privatization: Masses without congregations, baptisms, weddings, and encounters with the sick. I had a friend who related an experience of a priest saying a “private” Mass (literally) at the parish-scheduled time and sending an acolyte into the church to announce Communion would be distributed within a few minutes.