I am astonished at the number of clergy and professional musicians in the service of Catholic churches who are ignorant of the proper place of hymnody in the Catholic liturgy. With the exception of the Gloria and the Sanctus (hymns in the very broad sense of the term), and of the Sequences sung for Easter, Pentecost, Corpus Christi, and Our Lady of Sorrows, hymns, as such, are entirely foreign to the celebration of Holy Mass. In the Divine Office, however, there is a metrical hymn at every Hour. Hymns, then, properly belong to the Liturgy of the Hours, while sung dialogues, antiphons, psalmody, and acclamations belong to the Mass.
The standard hymn singing that characterizes Protestant (or protestantized) worship is performed in a relatively uniform and congregational manner. The liturgical chant of our Catholic tradition, on the other hand, privileges the responsorial, dialogical, antiphonal and acclamatory modes of performance. These, being among the most effective forms of actual sung participation, manifest more adequately the mystery of the Church as a Eucharistic organism of different members, characterized by "the order of symphony, an order in liberty and in love." The way we sing at Mass effectively shapes one's understanding -- or misunderstanding -- of the Church, of the priesthood, and of the hierarchical ordering of the liturgical assembly. A protestantized approach to music at Mass will inevitably engender a protestantized ecclesiology.
Sing the Liturgy Itself
A composition that does not belong to the liturgy and lead more deeply into the mystery celebrated, even though it be sung with full-voiced enthusiasm by all, cannot be qualified a true expression of conscious and active participation in the liturgical action. Active participation implies that the assembly is singing the liturgy itself, beginning with the dialogical chants, acclamations and refrains.