A Good Friday Connection with Mozart

My brother and I are separated by the Atlantic Ocean and a good chunk of Europe on Good Friday 2018.

Eastern Passage-Merton-Barth-Mozart-Vienna

I have been reading some of Thomas Merton's "Conjectures of a Guilty Bystander". He offers a conjecture on "Barth's Dream" wherein the Protestant theologian encounters a comment by Mozart that references the phrase from Catholic Eucharistic liturgy "Agnus Dei qui tollis peccata mundi". While attending Good Friday service at St Andrew's Parish in Eastern Passage, I noticed that this phrase is the text in the stained glass window above the altar. My brother and sister-in-law are spending Good Friday in Vienna, where Mozart worked and died. 
References

(n.d.). Mozart: The Man and the Artist Revealed in His Own Words. Retrieved March 30, 2018, from https://books.google.com/books?id=uWQ4DQAAQBAJ&pg=PA99&lpg=PA99&dq=Protestants+did+not+know+the+meaning+of+Agnus+Dei+qui+tollis+peccata+mundi&source=bl&ots=yO7L4T0qbj&sig=bFPvSaOOUFbUZ65gPKC3IceYBoU&hl=en

Merton, T. (2014). Conjectures of a guilty bystander. Garden City, NY: Image Books.