I have suspicions on the meaning of this dream, but I'd like to get more opinions:

At first I am watching a movie where in a large room, hundreds of dead bodies have been laid out, wrapped in cloth. (Possibly a church?) Dream shifts to where the movie is now reality.  I don't seem to have strong feelings about the bodies either way.  At some point I begin singing "O Holy night", and discover that the dead are singing with me.  They are now standing and fully restored. (Note - I'm not religious in the slightest.  Not my thing.)  So we finish the song and I exit the building.  On the way out someone is walking up (my boss I believe).  I must have figured that what happened inside with the dead people was something imaginary, or at least ghostly, because I warn this person not to go inside because of what she will see.  Despite my warning, the door is opened.  I peer inside too and see that all the bodies are still wrapped in cloth. However, this time they're moving - ostensibly coming back to life. My feeling now is one of amazement. The dream ends.

Hi, this is what your dream might mean...

Watching a television (movie or show) implies you're trying first to get an objective perspective on the issue, but that also means it's rather emotionless. So, that's why you next experience it as if you're in the movie. Dead people may indicate characterisations of you that you thought of as something you grew past. Now, the dead aren't supposed to be singing, but knowing these characterstics of yours aren't as dead as you supposed doesn't bother you much. It's only when somebody else sees them not-fully-dead that you become worried... of what they might think, because it might unsettle them to discover this of you.

Excellent interpretation!  I'm still trying to figure out specifically what the metaphor is.  But, the logic of what you suggest is very sound.