"The traditionally appropriate musical instrument of the Church is the organ, which, by reason of its extraordinary grandeur and majesty, has been considered a worthy adjunct to the Liturgy, whether for accompanying the chant or, when the choir is silent, for playing harmonious music at the prescribed times … Let our churches resound with organ-music that gives expression to the majesty of the edifice and breathes the sacredness of the religious rites; in this way will the art both of those who build the organs and of those who play them flourish afresh and render effective service to the sacred liturgy." — Pius XI, Divini Cultus (1928).
Recently, there has been some discussion in our parish about the organ postlude and its liturgical function. So, I’d like to take this opportunity to explain why the playing of a postlude is, indeed, a beautiful practice that compliments the liturgy. The organ, throughout the history of the church, has served a role greater than simply accompanying singing. In its range and color, it power and it's beauty, it represents the person of God in a very profound way. The organ postlude is its final prayer, usually one of joy and praise. Traditionally, the postlude is a piece of music that both gives voice to the immense joy in our hearts when we receive the Eucharist and fills us with energy to go out and bring what we have received in mass to others. Therefore, it should generally be a piece that is more energetic and spirited.
To quote a wonderful article from Corpus Christi Watershed, the postlude "is highly appropriate for a time of thanksgiving, because throughout the Mass we have been preparing ourselves, with contrition, with steps towards the altar, with much earnest prayer and supplication, and when the Lord finally makes Himself present to us and even gives Himself to us in Holy Communion, our hearts should be bursting and ready to cry out “Alleluia!” with all of creation. That is what an organ postlude does better than anything else can do: it makes creation resound with the divine praises as we get ready to step forth into the world again."
That is not to say, however, that the postlude is always loud and energetic in its entirety. There are some feasts that commend themselves to a softer, more meditative postlude. For example, one of my favorite postludes during Christmas time is Olivier Messiaen’s “Les enfants de Diu,” or “the children of God.” This piece begins with lots of energy and volume, but it ends with a sweet meditation played on the softest of strings.
In a similar vein, I believe the postlude to be complimentary to silent prayer, not a foe to it. Throughout the mass, we have opportunities to reflect in silence and quiet prayer, most importantly right after the reception of Holy Communion. After the final blessing, we are sent forth, and the postlude encourages us to do just that. There is, of course, nothing wrong with silent prayer and thanksgiving after mass; I suggest, for all those who remain to pray after mass, that you allow yourself to pray with the organ. We are blessed with a lovely instrument here at our parish: we ought to allow its many colors to guide and inspire our prayers at the end of mass, and invigorate us to go out and spread the Gospel. During this season of lent there is, however, no postlude, as the church asks for the organ to be silent.
The church has much to say about the organ: to conclude, I commend to you these excerpts about the organ and liturgy from the Church:
"Among the musical instruments that have a place in church the organ rightly holds the principal position, since it is especially fitted for the sacred chants and sacred rites. It adds a wonderful splendor and a special magnificence to the ceremonies of the Church. It moves the souls of the faithful by the grandeur and sweetness of its tones. It gives minds an almost heavenly joy and it lifts them up powerfully to God and to higher things. — Pius XII, Musicae Sacrae (1955)."
"In the Latin Church the pipe organ is to be held in high esteem, for it is the traditional musical instrument which adds a wonderful splendor to the Church’s ceremonies and powerfully lifts up man’s mind to God and to higher things. — Vatican II, Sacrosanctum Concilium (1963)