Agnus dei, qui tollis peccata mundi, miserere nobis
Now, I've only studied classical Latin, so forgive me if this is stupid question for students of the medieval variety, but shouldn't it be a vocative: agne dei? I'm not suggesting the grammar police go after a centuries-old piece of liturgical text, just wondering whether there's a reason for the nominative, considering the "lamb" is being addressed, as evidenced by the 2nd person tollis.
Thanks, and again, sorry if this is a stupid question. I'm trying to write an essay on Descartes at the same time and study for an Arabic midterm.