Why do some priests sing so many Mass prayers, when other times, they don’t? Singing the prayers of Mass is not a new thing. But before the Mass was reformed in 1970, after Vatican II, it was very unusual for people to experience Mass that way. Since Vatican II, there are very few rules about singing.
First, a little history. In the Traditional Latin Mass, for centuries there have been three distinct ways the Mass is celebrated. And, important to explain, the priest is not free to “mix and match.”
The “highest” is the solemn high Mass, which in practice involved several priests, plus several well-trained altar servers, plus a choir. Because of the complexities of this, most Catholics never experienced this. Then there was what was called a “sung” Mass, which required only a priest, but it still required a good number of experienced altar servers and a choir. And it also meant that the priest had to sing a lot of the Mass. So this, too, was not so common; although many parishes would have one such Mass each Sunday. Finally was the “low” Mass, in which there is one priest and one altar server; but no choir. None of the prayers are sung; and with no choir, it resulted in a lot of silence. This was the Mass most people experienced for a long time, with the possible addition, in some places, of the people singing some hymns.
While the low Mass, just described, was the most common experience for many centuries, it was never the “ideal” way. It was an adaptation, given the realities in many places, where all the things needed for a full, “high” Mass weren’t available. Over the course of the 20th century, there was a movement to try to renew the Church’s worship. This led to reforms under Pope Pius X, Pope Pius XII, and of course, in association with Vatican II.
When Pope Paul VI presented a “new” Mass to the Church, there was a largely new approach to when and how the Mass could be sung. First, there was more emphasis on the people singing parts of the Mass, such as the Gloria, the Creed, the Sanctus, the Our Father, the Lamb of God, etc. (Not that the people couldn’t sing these before.) Second, the priest has many more options about singing his prayers. Before it was an all-or-nothing approach. Today the priest is basically free to chant some parts, but not others. One guideline is known as “progressive solemnity”; meaning that where an occasion is more solemn, the Mass should be celebrated in a “higher” fashion, and singing the prayers can help convey that.
If you wonder why some priests sing more and others less, it’s not hard to figure out. Some of this is how we were taught; and also, some of us feel more at ease doing so. Many priests will flat-out tell you, they don’t sing very well, so they want to spare you! Yet it is still the case that the Church treats singing the Mass as its fullest, ideal form; and it is a fact that every single prayer of the Mass, even the readings, can be sung.