Q: Two questions related to the translation of the Agnus Dei.
1. The Latin has “peccata mundi” – which is plural; yet the source text (John 1:29) is singular (including in the Clementine and neo-Vulgates). Why the difference / change?
2. It makes sense that in the English Missal it is also translated in the plural (since the liturgical source text is plural)… but in the Spanish Missal it is in the singular. Why?
1. To answer that adequately, we’d have to ask the author of the Liber Pontificalis, who ascribed the origins of the Lamb of God to Pope Sergius in the 8th century. I treat this in my book At the Supper of the Lamb.
The simplest answer is that this is a liturgical text based on scripture, not a reading from scripture. The same thing happens in the Gloria: “sins of the world.”
Composers today make similar choices with impunity when giving us a hymn like “On Eagle’s Wings” or “Shepherd Me, O God.” They aren’t quoting the bible exactly, but they are interpreting the biblical text and applying it to a contemporary need.
I suspect that the 8th century church took consolation that Christ forgave not just the general sin of the world but the personal sins of those now presenting themselves for communion.
Some Catholics still may be too strict in withdrawing themselves from the communion line. This brief litany is a reminder that forgiveness is theirs, as is the Eucharist.
2. With regard to the Spanish Missal:
The rules for translation were not as strict 50 years ago as they are now. The revised English translation for the missal’s third edition had to adhere more closely to the Latin. In general, it was thought that the Spanish translation was already closer to the Latin, so its Order of Mass went into the third edition virtually unchanged. This resulted in a number of surprises to English speakers.
I wrote an article on this for the “Amen Corner”: http://paulturner.org/wp-content/uploads/2015/11/Amen-Corner-misal-romano.pdf