Here is a debatable topic. Many are divided on it.
Paragraph 103 states that, “among the faithful, the schola cantorum or choir exorcises its own liturgical function.” It equates the those two terms. I argue that what they mean by choir and what we mean by a schola are slightly different things.
Here we are getting into opinion land so hold on to your hat. (Does anyone get the picture reference?) Everyone agrees that we need a group of people to sing at the Mass. Most parishes, I would argue, have a parish choir. By and large, the purpose of the choir is to lead congregational singing. This idea has been enshrined in much of our newer liturgical architecture. There is no choir loft or ideal placement of the choir to give an optimal experience of the music they produce. There has a choir “designated area” pretty close to being at the same level as the rest of the congregation, and with luck they are centrally located so the experience is heard evenly (instead of one side being blasted by the choir and the other being far away.) In these churches, one can get away with doing a choral piece, but you are fighting poor placement and poor acoustics.
This is good, serviceable, and worthy as far as it goes. Most parishes survive just fine with a choir consisting of a group of people who help bolster the singing of the congregation.
A schola does this also but is expected to do more. “It’s purpose is to take care of the parts proper to it.” As we have explored, there are many things that it is possible for the choir to do alone, or in back and forth with the congregation in addition to simply assisting the congregation. There are the propers of the Mass to be sung (such as the introit) and the tradition of chant to be upheld and fostered. The schola takes the music to the next level, not merely supporting but by expanding the musical experience to express a greater depth and width of the Church’s Tradition. It educates. It becomes a ministry similar to that of a lector, itself proclaiming the Word and giving sung instruction in the Christian life to be heard, digested, and applied. (Which is why they should be as good as they can be in any particular parish, not merely good enough.) With this in mind we understand church architecture that places the choir in the building in such a way that they are most easily heard and understood with acoustics suitable for the production of music.
Okay. Enough of my opinion.
In general, this paragraph says, the norms for the schola apply equally to other musicians with a special emphasis on the organist, once again giving emphasis that the primary instrument of the Catholic Church is the pipe organ.