I'm Jewish and I sing in a choir. AFAIK there are no other Jews in the choir. We are going to hold a carol concert.
I wouldn't sing at a carol service, but this is a concert, so to my mind it is not a religious service. As far as I am concerned, I don't particularly care about the words I am singing, they're not offensive to anybody, it's just an opportunity for sharing the pleasure of music.
Would this attitude be offensive to Christians?