We are edging closer to that time in the liturgical calendar when only but our voices can decorate the Liturgy. The music proper to the Liturgy, said Saint Pius X, is purely vocal, when he discussed the subject of musical accompaniment in Tra le sollecitudine. Organs and similar pneumatic instruments—percussions have long been forbidden—in terms of chronology, are a novelty in Catholic worship. As late as the mid-18th century, the papal choir in the Sistine Chapel had not yet admitted the organ into its praxis. In a way, just as the sacrifices we offer and the discipline we undergo during Lent assist us in recovering our humanity, so the Church’s abstinence from the organ during Lent demonstrates as well, actuose potius quam symbolice, a return to the simplicity of her worship.
The whole Christian world indeed still does not accept the use of the organ and of other musical instruments; for, besides the Russians of the Greek Rite, who have neither organ nor other instruments of music in their churches, Father [Pierre] Lebrun bearing witness in vol. 2 of the Explication de la Messe, p. 215, Our Pontifical Choir, as is known to all, admits polyphonic—yet grave, seemly and devout—music, but it never admits the organ, which is even noticed by Father [Jean] Mabillon in his Musaeum Italicum, vol. 1, p. 47, § 17: On Trinity Sunday, we were present in the Pontifical Chapel, as they call it, etc. No usage of organ music in the Holy Mysteries of this wise is admitted, but vocal music alone, and this one being grave with plainchant.
Universus quidem Orbis Christianus Organi aliorumque musicorum instrumentorum usum adhuc non recepit ; praeter enim Ruthenos Ritus Graeci, qui in suis Ecclesiis neque organum neque alia musicae instrumenta habent, teste Patre Le Brun tom. 2 Explication. Miss., pag. 215, Nostra Pontificia Cappella, ut omnibus notum est, cantum musicum, sed gravem, decorum piumque admittit, nunquam autem organum recepit, quod etiam notatur a Patre Mabillone in suo Musaeo Italico, tom. 1, pag. 47, § 17, Dominica Trinitatis, Cappellae, ut vocant, Pontificiae interfuimus, etc. Nullus organorum musicorum usus in huiusmodi sacris, sed sola vocum musica, eaque gravis cum plano cantu admittitur.
The organum pneumaticum will soon not be pulsated, but the organa vocis, the organs of our voice, will never cease to resound, as they had never been for once since the dawn of Christendom consigned to the province of silence.
Ut in omnibus laudetur Dominus.
Reference: Benedict Pp. XIV, Encyclical Letter Annus qui hunc, 3, near the beginning.