The Credo is the longest part of Schubert’s Mass in G. It is also my favorite.
Musically, it breaks down into an A-B-A pattern: first a gentle contemplation of the Trinity, then a dramatic section on the life of Christ, followed by a return to the Trinity, human salvation, and eternal life.
One can imagine this structure in terms of two worlds, or two levels of being, the divine and the human. It begins on the divine level of God’s inner life, the eternal “begetting” of the Son, which is marked by the almost dance-like rhythm of the words Deum de Deo, Lumen de Lumine, Deum verum de Deo vero. Then there is a dramatic tension that starts with Qui propter nos homines that is, on behalf of man, the Son becomes flesh. This is part ‘A’.
In part ‘B’, the Son of God enters all the drama, pain and glory of human existence, through his death (passus et sepultus est), to victory (et resurrexit teria dia), looking forward to the end of human history (cuius regni non erat finis).
Suddenly the music takes us back to part ‘A’ the calm of the divine world and the inner life of God, with the words credo in Spiritu Sancto. But the Holy Spirit also has a role in human affairs, hence the slight tension when speaking of how he inspires the prophets, the necessity of baptism, which are how the Spirit guides humanity to eternal life – et vitam aeternam saeculi.
It is a musical expression of the Christian’s grand vision of reality, the “exitus and reditus” of all reality from and towards God. Out of his own inner dynamism God creates the world, and then he enters his world in order to unite it to himself.