Ordinarily the chants of the Mass ought to be sung, whether in the Ordinary or the Extraordinary Form.
On those occasions when hymns are sung at Mass–and let’s be honest, we all do it–how do we choose among the hundreds of thousands of hymns available?
Pope Benedict XVI addressed this question in his post-synodal Exhortation Sacramentum Caritatis, paragraph 42:
In the ars celebrandi,liturgical song has a pre-eminent place. Saint Augustine rightly says in a famous sermon that “the new man sings a new song. Singing is an expression of joy and, if we consider the matter, an expression of love.” The People of God assembled for the liturgy sings the praises of God. In the course of her two-thousand-year history, the Church has created, and still creates, music and songs which represent a rich patrimony of faith and love. This heritage must not be lost. Certainly as far as the liturgy is concerned, we cannot say that one song is as good as another. Generic improvisation or the introduction of musical genres which fail to respect the meaning of the liturgy should be avoided. As an element of the liturgy, song should be well integrated into the overall celebration. Consequently everything — texts, music, execution — ought to correspond to the meaning of the mystery being celebrated, the structure of the rite and the liturgical seasons. Finally, while respecting various styles and different and highly praiseworthy traditions, I desire, in accordance with the request advanced by the Synod Fathers, that Gregorian chant be suitably esteemed and employed as the chant proper to the Roman liturgy.
Some would say that the best examples of hymns are those that imitate the proper texts themselves.
Others might say that the best hymns for Mass are the rich patrimony of office hymns.
The problem with these two ideals are that they leave out most of the hymns that are actually sung in the best English-speaking music programs in the Church–another kind of ideal, and also compelling: the exemplars of our own time. Hymns like Praise to the Lord, Holy God (a versification of the great hymn Te Deum), Holy Holy Holy, and Come Down O Love Divine are neither office hymns nor textually nor musically close to the proper texts. Does this mean they are unsuited for liturgy, or are they part of the patrimony?