a one line melody
I think he didn't want singers to get to fancy with individual variations and distract from the purpose of the mass.
The word 'chant' has several uses: 1: recite with musical intonation; recite as a chant or a psalm; 2: a repetitive song in which as many syllables as necessary are assigned to a single tone; 3:...
This is a little ambitious, don't you think? Rome wasn't built in a day...
A greek prayer, Kyrie eleison (Κύριε ελέησον), meaning "LORD, have mercy," that is often sung in Mass.