The Mass for Four Voices (1592-1593) was likely the first of the three great unaccompanied polyphonic mass settings Byrd composed in the 1590s. All three masses are settings of the Ordinary: Kyrie, Gloria, Credo, Sanctus, and Agnus Dei. The scoring of the Mass for Four Voices is often thought to consist of the usual soprano, alto, tenor, and bass, but the closeness of the alto and tenor parts has led some authorities to believe that alto, tenor, baritone, and bass achieves a more satisfactory balance.
Like its fellows, this mass was composed for liturgical use by Byrd's fellow Catholics -- a dangerous proposition, since celebration of the Catholic mass was forbidden in Elizabethan England under threat of severe penalties. The central act of the liturgy was therefore performed by Catholics, or recusants as they were termed, under conditions of strict secrecy. These conditions are reflected in Byrd's three settings, which entirely eschew the kind of exuberance and florid writing encountered in earlier Tudor settings of the mass. Instead, Byrd's contrapuntal writing is largely syllabic, with the lines treated to clean, clear imitative counterpoint. Byrd compensates for such implications of austerity with a superbly expressive setting that often points up key words or sections of the text in a manner rarely encountered in settings of the timeless and unchanging words of the Ordinary. Examples include the soaring lines at "et ascendit" (and ascended into Heaven), or the sublime beauty of the Agnus Dei, in which Byrd gradually builds the number of voices and complexity of the counterpoint to achieve a searing climax at the words "dona nobis pacem" (grant us Thy peace). Perhaps he was making a political plea on behalf of all persecuted Catholics, who could emerge into the light only with the brightness of the work's very last sonority.