Sin

Sin \sin\ noun;
1. Transgression of divine law
2. Any act regarded as such a transgression, especially a willful or deliberate violation of some religious or moral principle
3. Any reprehensible or regrettable action, behavior, lapse, etc.; great fault or offense

The origin of sin is Old English synn ("moral wrongdoing, offense against God, misdeed") from Proto-Germanic *sundjo ("true"), which derives from Proto-Indo-European *es-ont-, the preposition of the base *es- ("to be"). How exactly "true" became "misdeed" is attributed in part to the notion of "to be truly the one (who is guilty)" and in part to the phrase "it is being" in the Hittite confession formula. Some etymologist disagree with all this and think that the Proto-Germanic word was a borrowing from Latin sontis ("guilty, criminal").

The reason I wanted to talk about sin today is because I noticed that in the Catholic mass, sin is referred to as a mass noun* in one part of the mass but a count noun in (I believe) every other context. Furthering the conundrum, the phrase in which sin appears to be a mass noun is virtually identical to a phrase used later in the mass where it's a count noun:
In the Gloria hymn we sing, "...Lord God, Lamb of God, you take away the sin of the world..." But, during the breaking of the bread we say/sing, "Lamb of God, you take away the sins of the world..."¹
This seemed strange to me because generally nouns are either mass or counted, but not both. There are exceptions, of course, but different usages are confined to specific contexts. Here, the contexts appear to be exactly the same. My best guess is that in the Gloria phrase sin is being equated with evil, and in all the other contexts it is being treated as a discrete, countable "act regarded as a transgression of divine law."

Thoughts?

*A mass noun is one that can't be counted (water, air, etc.) and count noun is one that can (shoe, peach, etc.)
¹http://catholic-resources.org/ChurchDocs/Mass.htm