Which person or group brought polyphonic music into the christian church?
No context provided
Who wrote the oldest known polyphonic setting of the mass attributable to one composer and brought it into the Christian church?
Guillaume de Machaut
No context provided
Who first brought polyphonic music into the Christian church?
unknown
Polyphony
https://en.wikipedia.org/wiki/Polyphony
Church music
https://en.wikipedia.org/wiki/Church%20music
Although the exact origins of polyphony in the Western church traditions are unknown, the treatises Musica enchiriadis and Scolica enchiriadis, both dating from c. 900, are usually considered the oldest extant written examples of polyphony.
Polyphony
The oldest extant polyphonic setting of the mass attributable to one composer is Guillaume de Machaut's Messe de Nostre Dame, dated to 1364, during the pontificate of Pope Urban V. The Second Vatican Council said Gregorian chant should be the focus of liturgical services, without excluding other forms of sacred music, including polyphony.
Polyphony
Musica enchiriadis is an anonymous musical treatise of the 9th century. It is the first surviving attempt to set up a system of rules for polyphony in western art music.
Musica enchiriadis
Scolica enchiriadis is an anonymous ninth-century music theory treatise and commentary on its companion work, the Musica enchiriadis.
Scolica enchiriadis
The exact origins of polyphony in the Western church traditions are unknown, in part because the oldest extant written examples of polyphony were composed anonymously. However, the first instance of polyphonic church music attributed to a single named composer occurred when Guillaume de Machaut wrote Messe de Nostre Dame in 1364, during the pontificate of Pope Urban V.