One can walk into nearly any parish today and hear almost any type of music, from Gregorian chant to folk music to heavy metal. While most parishes offer one type of music within a given Mass, some parishes even provide a musical contrast within the same one. I actually attended a funeral Mass in which an electric guitar was used alternately with a harp. Figure that one out if you can.
Unusual combinations aside, isn’t it a good thing to have something different for everyone? The old people can listen to chant, the middle-aged people can listen to folk music, and the young people can listen to heavy metal. Everyone gets to be around their favorite music, which is, after all, a large part of what the Mass is all about: personal preferences and self-expression. Right?
Wrong.
Pope Benedict XVI, then Cardinal Ratzinger, stated in The Spirit of the Liturgy that "Not every kind of music can have a place in Christian worship." Although individuals can be naturally drawn to certain types of 
music, sacred music–which is meant specifically for the liturgy — is not derived from natural tendencies or preferences. Sacred music, like the rest of the liturgy, is not about mere self-expression; it is about receiving and participating in what has been passed down to us, such as Gregorian chant.
Gregorian chant — named after Pope St. Gregory the Great (590-604) — is sacred music of the highest order. In the Second Vatican Council’s Constitution on the Sacred Liturgy, Sacrosanctum Concilium , we are told that
The Church acknowledges Gregorian chant as specially suited to the Roman liturgy: therefore, other things being equal, it should be given pride of place in liturgical services (Art. 116).
Why does Gregorian chant occupy such a central role in the liturgy? Pope St. Pius X (1903-1914) explains in his 1903 instruction Tra le Sollecitudini that
Sacred music should…possess, in the highest degree, the qualities proper to the liturgy, and in particular sanctity and goodness of form, which will spontaneously produce the final quality of universality (No. 2).
The saintly Pontiff goes on to state in the same document that
These qualities [of sanctity, goodness of form, and universality] are to be found, in the highest degree, in Gregorian Chant, which is consequently the Chant proper to the Roman Church, the only chant she has inherited from the ancient Fathers, which she has jealously guarded for centuries in her liturgical codices, which she directly proposes to the faithful as her own, which she prescribes exclusively for some parts of the liturgy… (No.3).
While other types of sacred music (such as polyphony) may be admitted to the liturgy (SC Art 116), Gregorian chant is, according to Pope St. Pius X, "the supreme model for sacred music" (TS No. 3) because of its sanctity, goodness of form, and universality. It has a simplicity, sobriety, and resonance that manifest the beauty of the liturgical action.
The next time you’re at Mass, ask yourself how the music you’re hearing measures up to this supreme model. In many parishes, the goal seems to be the avoidance of this supreme model, rather than the approach toward it. In fact, many Catholics would be surprised to learn that Church authorities have taught anything at all on sacred music, and would probably be even more surprised to learn that specific musical instruments have been named, whether for endorsement or for exclusion.
One of the instruments that has been mentioned is the pipe organ, which can enhance the beauty of Gregorian chant. According to the Council Fathers, 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." (SC Art. 120). The pipe organ, however, is meant to accompany the singing, not to overpower it.
This "non-overpowering rule" is applicable to any other instruments which might be lawfully admitted into the liturgy, pending the approval of rightful authority (SC Art. 120). It is also pointed out that
This [admittance of other instruments] may be done, however, only on condition that the instruments are suitable, or can be made suitable, for sacred use, accord with the dignity of the temple, and truly contribute to the edification of the faithful (SC Art.120).
Can drums, guitars, and pianos be made suitable for sacred use? Do they accord with the dignity of the temple? Do they contribute to the edification of the faithful? Before these questions are answered, it should be pointed out that while many types of music are inherently good, they are not meant specifically for the Mass. Piano music, for example, can be great entertainment at a social function–but the Mass is not a mere social function, it is the Sacrifice of Our Lord Jesus Christ.
With this in mind, it is interesting to note that Pope St. Pius X actually banned pianos and drums from the Mass, stating that "The employment of the piano is forbidden in church, as is…that of noisy…instruments such as drums…" (TS No. 19). We can be fairly certain that, had guitars made their way into the liturgy by 1903, our Holy Father would have banned them as well.
This is not to say that such music is inherently bad, but that it is not meant specifically for the liturgy. There is a type of music which, although not appropriate for the liturgy and therefore not called "sacred," is used to teach the Faith and is therefore called "religious". Pope Pius XII (1939-1958) said that
We must also hold in honor that music which is not primarily a part of the sacred liturgy, but which by its power and purpose greatly aids religion. This music is therefore rightly called religious music. The Church has possessed such music from the beginning and it has developed happily under the Church’s auspices. As experience shows, it can exercise great and salutary force and power on the souls of the faithful…when it is used…during non-liturgical services and ceremonies… (Musicae Sacrae No. 36)
Although he does not give specific examples, perhaps Silent Night or We Three Kings of Orient Are — sung in the vernacular–would be examples of such songs which, according to the Pope,
… bring pure and chaste joy to young people and adults during times of recreation …They bring pious joy, sweet consolation and spiritual progress to Christian families themselves. Hence these popular religious hymns are of great help to the Catholic apostolate and should be carefully cultivated and promoted (MS No. 37).
We are told that popular religious hymns should be promoted–but not in the liturgy. Everything good has its place, but the Mass is not the place for everything good.
There is no better way to sum it up than with the words of our Holy Father, Pope Benedict XVI, from his 2007 encyclical Sacramentum Caritatis :
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… that Gregorian chant be suitably esteemed and employed as the chant proper to the Roman liturgy …(No. 42).
We have the clear instructions, now we need more people to read them and carry them out. St. Cecilia, Patroness of Musicians, pray with us that this will happen, for the glory of God and the sanctification of all.
(For more information on sacred music, read Papal Legislation on Sacred Music . Help support Catholic Exchange buy getting Papal Legislation on Sacred Music and The Spirit of the Liturgy from our online store.)