The reason the Catholic Mass is a great mystery to many, and always was and must remain one, is because it is rich in symbolism and ritual. Its many layers of meaning cannot be stripped away without reducing its impact. At its core are mysteries which cannot be adequately understood or conveyed by human language and intellect. Compare the Mystery of the Holy Trinity or the Byzantine term for the Sacraments, Holy Mysteries. The nature of the Mass is mystery itself! And if you think about it, repetition does not add to the mystery but actually contributes to exposition. Repetitions point to the parts which are really important. We repeat the antiphon of the Responsorial Psalm because it contains a central Truth about God. We repeat the Agnus Dei in adoration and worship of Christ who has redeemed us. In the Extraordinary Form, many more things are repeated, because they were central and important to the Eucharist. Are they no longer central and important? Have we sacrificed the teaching ability of repetition for the luxury of getting back to our cars in the parking lot after only one hour of worship? I don’t know.
In addition to the need for emphasis and teaching the importance of parts, we must not forget the utility of repetition for fostering meditation. This is the core of devotions such as the Rosary. We are commanded to meditate upon the mysteries while repeating these easily-memorized prayers. Therefore we enter more deeply into the Life of Christ. For those who do not understand Latin, surely it is even easier to find a meditative state while the prayers are being repeated, that allows us to unite ourselves with the Sacrifice of Calvary. As a choir member I often concentrate heavily on how many times I have recited the Agnus Dei so that I do it correctly and lead others to do the same, but I hope that we are also meditating on the great gift of the Eucharist which we are about to receive, because we all know the content of the prayer and what it means already.
In a way, the Mass itself is repetition, as there are parts that never change, and parts that cycle throughout the weeks and years. If we truly believed that repetition was useless then we would only go to Mass on special occasions. Surely repetition is good for the soul as it provides structure and discipline which we can rely on.