One writen by Martin Luther, or John Calvin. They didn't used to be allowed. They were the only things I missed after I converted in 1958. When we first started having hymns in the Catholic church (Low Mass) they seemed unsingable to my ear. Whole orders of priests, monks, and nuns wrote "new" hymns after 1965. We are still singing them today, and they seem to have relaxed the rule against "Protestant" songs.
However, at Newman Club at the University of CA, Berkeley, the priests used the "Congregational High Mass". It was sung all in Latin and sounded like Gregorian chant to me. I loved that. The space where they said Mass was upstairs. If you were a little bit late and they had started before you cimbed the stairs, the music afting down the stairs was simply heavenly.
I never found another church, after I married, that used that Mass, and I really missed it.
One writen by Martin Luther, or John Calvin.
Stop the bus. You've attended masses where Luther's A Mighty Fortess Is Our God and hymns from Calvin's Genevan Psalter have been sung?