Polyphonic chant is a type of Christian devotional singing developed in the 10th century where two or more melodies or parts are sung together in a composition.
As with anything new, not everyone approved of polyphony.
Some believed that melodic complexity was the work of the devil, who tried to seduce believers through the sin of pride. Pope John XX II was dead against polyphony and in 1324 CE warned his flock not to fall into the satanic lure of musical innovation.
However, such narrow-mindedness couldn’t stop the flow of musical evolution.