The "mass for pope Marcellus," by Giovanni Pierluigi da Palestrina (1525-94), is one of the highest achievements of Renaissance sacred music, as spiritually overpowering as it is musically exquisite. Stephen thinks of both the paradoxical achievement of the music ("the voices blended, singing alone loud in affirmation") and its religious significance ("and behind their chant the vigilant angel of the church militant disarmed and menaced her heresiarchs"). These two things—the tension between monophonic chant and polyphony, and questions of orthodoxy and heresy—were intimately linked in the composer's mind, and Stephen seems to be pondering their relevance to his own literary art.
Stephen imagines that, behind the voices of the singers, the Archangel Michael (“the vigilant angel”) stands menacing all those who would endanger Christian verities. This fancy almost certainly reflects a mid-16th century debate about the acceptable limits of religious music. Gifford and Seidman observe that Michael was often invoked in the Catholic church’s struggle against Protestantism in the 16th century. One aspect of this struggle was a Counter-Reformation effort to purify sacred music. The Council of Trent (1545-63) issued decrees against “music in which anything lascivious or impure was mixed,” and its sterner members argued that only plainsong (monophonic chant) should be allowed, as opposed to the polyphony (vocal music with multiple melodic lines) that had arisen from chant in the later Middle Ages and become highly popular in the Renaissance.
Palestrina was a brilliant practitioner of polyphonic composing, and his music was utterly dependent on church patronage. When Marcellus II died in 1555, his successor Paul IV immediately dismissed Palestrina from papal employment. But Paul's death in 1559 opened the holy see to Pius IV, who was more sympathetic to polyphony. In 1564, Gifford and Seidman note, Pius asked the composer to write “a polyphonic mass that would be free of all ‘impurities’ and would thus silence the purists. The Missa Papae Marcelli was that mass, and its performance succeeded in establishing polyphonic music (and Palestrina) as the voice of the Church.” Giuseppe Verdi said of the composer, “He is the real king of sacred music, and the Eternal Father of Italian music.” In James Joyce and the Making of Ulysses (1934), Joyce's friend Frank Budgen quotes him as saying "that in writing this Mass, Palestrina saved music for the church."
Putting all these details together, one can appreciate the "rare thought" that Stephen may be thinking here. He does not invoke Michael to affirm Christian faith. Nor is he using him as the sixteenth century counter-Reformation theologians did, as a symbol of the church's triumph over Protestant heresy. Instead, the righteous archangel standing behind the music represents Palestrina’s justification of his polyphonic art, religion having evolved into what Ellmann calls "a system of metaphors" for art in Joyce's mind. The way in which Stephen describes the choir’s singing of the Mass suggests that it represents a defense of aesthetic orthodoxy. The voices are “blended” (polyphonically diverse), but they sing “alone” in a kind of “chant” (like the multiple voices which join to make a single haunting voice in Gregorian plainsong).
Thus the mass is artistically innovative but still traditional, an intricately complex mixture of diverse elements yet still radiantly “pure.” It is quite plausible to imagine that Joyce heard in Palestrina's Mass something very similar to what he was attempting to do in Ulysses: carry venerable literary traditions like Homeric epic and Shakespearean tragedy forward into contemporary existence, and combine a kaleidoscopic multitude of subject matters and styles in a single aesthetically harmonious whole.
Gifford and Seidman note that Edward Martyn helped to generate enthusiasm for Palestrina and his Renaissance contemporaries in 1890s Dublin, and the mass for pope Marcellus was first performed at St. Teresa’s church in 1898. It is quite possible that Joyce attended this performance: he loved the lute songs of the English Renaissance, and in Penelope Molly thinks of having sung in a concert in "St Teresas hall Clarendon Street." The following seven audio clips present the mass in its entirety, usefully accompanied by the score. The third movement is the Credo, which Stephen has in mind when he thinks of the “Symbol of the apostles."
http://www.youtube.com/watch?v=7EhQ1eOfgwI&feature=youtu.be (Agnus Dei I)
http://www.youtube.com/watch?v=mGWNVrXlhew&feature=youtu.be (Agnus Dei II)