Pop music in different cultures uses some different instruments for example - around here it is not uncommon to hear bagpipes. Does this make them a pop instrument at heart? Probably not.
They’re not a pop instrument. There is record of them being used in church services for a long time. They are likely one of the instruments that Pope St. Pius X was referring to when he was talking about how wind instruments needed to be carefully regulated, but were allowed. A lone bagpiper at a solemn occasion is part of the normal music in a parish where the pipes are part of the cultural norm. The key here is that the use of the pipes in church music is ancient in custom, as the pipes themselves are almost as old as the church. The guitar is not, and its use in the church is a modern novelty, not part of a 1500 year cultural tradition. Similarly, it could be argued that the sitar might be appropriate in Indian churches, since it seems to have been part of the customary music of the Syro-Malabar Catholic Church since antiquity. Even though the sitar is outwardly similar to the guitar, it is part of their traditional liturgical culture, not a novelty of the past 40 years. Everyone needs to keep in mind that the 2000 year old tradition of Catholic music was never intended to be disturbed the way it has been, just as the liturgical tradition was not meant to be disturbed the way it has been (but that is for another thread). Tradition is the source of wisdom and the richness of our patrimony. To divorce ourselves from the past is to make us no longer *culturally *Catholic, even if we are still orthodox believers.
If they interpreted these documents as strictly as you seem to want to, in 1000 years there would be no guitars or pianos at mass, and the organ would still be the #1 instrument… I don’t think it really reflects the intent of the Holy See.
That seems to be the exact intention of the Holy See for the past thousand or so years. When polyphony got too complex and the use of too many instrumental lines and passages sung in the vernacular simultaneously with the Latin texts created chaos and confusion, they were told to simplify their music to conform with the past. When the music became increasingly operatic, they were told to stop writing stage music for church and simplify their music to conform with the past. Now we see the influence of rock, jazz, and other secular styles encroaching on the music and we again need to conform to the past. There have been other popular instruments that are not part of the church’s musical customs. The harpsichord was the dominant instrument in Western European music for two centuries. It was never a true part of the liturgical tradition and we don’t use it in church. The organ is not holy in its own right. It is just the custom of our church and it connects us with the past and with our roots. What is holy about it is that it is part of the tradition of the church that is itself holy. Tradition sanctifies the instrument. It’s not as if I think all organs go to heaven when they finally stop working.

The repeated call to return to chant and sacred polyphony does, however, imply that the music of the church is not to be influenced by passing fads of popular music, but to remain beautifully sacred in character musically as well as textually. Having a sacred text is not enough; it must sound like sacred music, which is to say like the Latin musical tradition of chant, polyphony, and traditional Latin hymns (which are actually chant). It may be in the vernacular, certainly, and may have been written that way rather than translated to it. But it ought to sound like the traditional music of our church, which means no guitars.
And as for the learning to play the organ thing, our church has two organists. They aren’t amazing, but they are passable. I know exactly the difference between playing the organ and the piano. I play piano and I’ve tinkered around on the organ. I know it takes time to learn to select the right stops and to manipulate the pedal keyboard, but it is worth it. And actually it’s like asking someone to switch from violin to mandolin, not trombone. They aren’t completely different-- the fingerings are all still the same. It’s just not the same technique. I’ve seen many people make the switch over successfully in the course of a semester. But then again, I was at music school, and they did practice every day.
As far as not having control over the music, that I will grant you. It is the problem I have lived with for all this time. You can talk to the music director and perhaps persuade him or her to try the real traditional music. Assuming the music director is a classically trained musician this is often an easy sell. But it’s much harder to get the liturgical committee to agree to the switch. That doesn’t mean it’s not worth fighting for, though. It is what we are supposed to be doing. The four hymn scene used at most churches, like receiving communion on the hand and using Eucharistic ministers to distribute communion, all results from the same basic misunderstanding-- that what was allowed as an exception should become the normal practice. All of these things are extraordinary. Allowed, but not normal, even if they are the most common approach.
What is normal to the Latin Rite is the introit chant (not an entrance hymn), the sung Kyrie and Gloria, the gradual (not a responsorial psalm), the alleluia, the offertory chant (not a hymn at the offertory, although there is room for a second piece of music after the offertory chant), the Credo, Sanctus, Agnus Dei, and the communion chant (followed by another piece of music, which could be a hymn). This is the tradition. The closing hymn is well within the normal tradition, since no music is prescribed to that place. The offertory and communion songs really belong as motets after the chant. And mass is supposed to start with the introit. In the rubrics, however, each of these places says that the Gregorian propers or another suitable piece may be used. It always mentions the propers by name, but always allows for an exception. The exception, however, has become the rule in most parishes. We have lost the chants. And that’s the problem. It’s not the guitars themselves that create the threat. It’s the fact that guitars are not suited for the proper music for mass, and that the music is selected to conform to the instruments rather than the instruments to the music. I would feel much differently about them, and regard them as sacred instruments if they were used to accompany the Gregorian chants in a manner in keeping with the tradition. To date, I have never heard this, and the secular nature of the guitar and piano has always been demonstrated with the secular music (note: not lyrics,
music) that they have performed.