Q: When I was young in my religious community there was an older priest who made a point of speaking softly or at least moving his lips when praying the Liturgy of the Hours by himself. Budding liturgy terrorists among us attributed that some sort of scrupulosity. Now, these many years later, I find that reading out loud can sometimes help me pay attention. So, my first question: prior to the renewal coming from the Second Vatican Council, was there either a canonical requirement or devotional practice regarding reading aloud.
Second: how about Mass? My understanding is that typically people at Mass quietly attended to their own devotions while the clergy and servers were at the altar. Again, my understand is that “high Mass” would have parts sung by the assembly and/or a choir, but the priest would also recite these texts on his own—often getting out of sync with the people because speaking is quicker than singing. Also, my understanding is that “dialogue Mass” with participation of the entire congregation was not a usual style of Mass anywhere prior to the renewal following the 21st ecumenical council. So, what were canonical requirements or devotional practice that guided the articulation by the priest or bishop at Mass?
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Q: I’m not sure about past canonical legislation, but I too know of older priests who followed the practice you describe. A question came to the Vatican’s Congregation for Divine Worship in 1973, and you can find the answer in Latin here on p. 150: https://www.cultodivino.va/content/dam/cultodivino/rivista-notitiae/1970/notitiae-09-(1973)/Notitiae-082-1973.pdf . It reassures that moving lips is not required for prayer.
Regarding Mass, again I’m not sure of legislation on this, but I understand that a priest was to recite everything, including the parts sung by the choir. Dialogue Masses began around the time of the liturgical reform.