On Sunday I had the pleasure of preaching at Grace Long Beach. I spoke on the Magnificat: "Revolutionary Joy" would have been a good title, though I didn't think of it till afterwards. Anyway, the audio is available here (the sermon starts at around 4:50).
This is the second time I've done a sermon with a sung refrain; I quite like this approach, for three reasons. (1) It creates a moment of embarrassment while everyone's trying to figure out why the preacher is singing so badly, and whether they ought to sing along; and I think a bit of public embarrassment can be a wholesome way of building community. (2) It helps to remind the congregation (or more importantly the preacher) that the sermon is part of the congregation's worship; it's not a lecture or a Bible study or an outpouring of pious emotion or whatever. And (3) it lets you offer a cluster of small related vignettes, instead of a sustained monologue. This really appeals to me when it comes to a colossal text like the Magnificat, a text that I'd find it almost impossible to speak about directly. There are some texts that matter so much that the best you can do is to glance at them indirectly, make a few mute gestures, sing an awkward little song in a crowded room.