I just thought I'd mention something peculiar and wonderful about the chant melody for this Sunday's Passion according to St. Matthew. In the narrator part, much of the music is very recitative-like on the syllables la-do-ti-la do (A-C-B-A-C). But every now and then, a wonderful melisma comes in: do-te-la-sol-fa (C-B flat-A-G-F). This is one of the most beautiful musical aspects of the Passion. (The Christus part, though, has the real gems.)
Now here's something important to keep in mind, dear narrators. When you sing that descending line, be sure that the B-flat is flat enough. It might even be good to exaggerate it a bit. You see, after all those B-naturals, that B-flat might not be as easily found as one might think.
So just keep that in mind.