Two things... I think a priest interrupting your performance to perform communion is no different than you interrupting his service to play a rocker!

And, I'm sorry, but although I am Christian, I would have no problem playing a Jewish hymn or song if requested...

You might also take a look at the history of the hymn Amazing Grace http://en.wikipedia.org/wiki/Amazing_Grace ... For any people that have come out of slavery, it's story should resonate.

BTW, I would also recommend the movie "Amazing Grace" which chronicles the anti-slavery movement in Britain. Very touching, and very apropos these days...