One of the more positive aspects of the American Bishops' recent document Sing to the Lord is its endorsement of the priest's singing of his parts of the liturgy:
No other single factor affects the liturgy as much as the attitude, style, and bearing of the priest celebrant. The importance of the priest's participation in the liturgy, especially by singing, cannot be overemphasized. The documents of the post-conciliar renewal repeatedly commend the ideal of a sung liturgy with sung dialogues between priest and people. (1)
When the priest sings his parts, the whole sung liturgy is integrated by this singing. Principal parts are introduced by dialogues between priest and people, which then form the point of departure for the continuing musical progress of the liturgy. When the priest sings his parts and the congregation sings their responses, their part in integral to the Mass, and when they go on to sing whole parts of the ordinary and to hear the choir sing parts of the proper, these parts, too, become as integral parts of the sacred action. Then, too, the subtle differences in style between the parts of the Gregorian Mass are effectively heard as a natural part of the sacred proceedings. Without the integration created by the priest's singing, the sung parts of choir and congregation seem more incidental.
But why should we have this fully sung liturgy? What is the most appropriate medium by which to address God in a formal liturgy? After the council, with the introduction of the vernacular and the stance of the priest at the altar facing the people, priests were often tempted to strike up a colloquial, conversational tone in an effort to engage the people, but this informal character tended to militate against the sacred and transcendent aspects of the liturgy, with the effect that too often the proceedings appeared to be merely a dialogue between priest and people, with little direct address to God. Moreover, the secular character of some of the music reinforced that horizontal dimension.
The singing element of the liturgy takes it out of the frame of the everyday; its elevated tone of voice aids in lifting the heart and the attention upward, where we envision God to dwell. The beautifully formulated prayers, lessons, and chants are a worthy means of addressing God, who is Beauty himself. The naturally rhythmic character of singing unites the voices of the congregation, joining them to an act of transcendent beauty, drawing them upward in the singing of it. For the moment they are taken out of the everyday, temporarily set aside for the most important thing they can do, the worship of God, and this is the essence of the sacred. What a joy for a congregation, to be incorporated into a worthy and beautiful act of worship! The singing celebrant is thus the keystone of such a beautiful liturgy.
This manner of celebrating a completely sung Mass was integral to the tradition. The normative form of the Mass was the high Mass, in which everything to be said aloud was sung. it must be acknowledged that before electronic amplification, singing was the way to project the priest's voice through a live church; it was a practical necessity. But it must also be acknowledged that this is only a part of the picture--the elements of beauty, transcendence, and the sacred are essential aspects of that same singing. In the 1940s Marshall McLuhan said that the microphone would be the death of the Latin Mass, a very astute and prophetic observation.
The Second Vatican Council reiterated the principle of a completely sung Mass:
A liturgical service takes on a nobler aspect when the rites are celebrated with singing, the sacred ministers take their parts in them, and the faithful actively participate. (2)
And Musicam sacram spelled it out:
The distinction between the solemn, the high, and the low Mass ... remains in force, according to tradition and current law. …