Anybody have any clue on what THIS movie is about?

The plot of Tosca explains everything:
In the opera "Tosca," Tosca is a singer in Rome during the Napoleonic Era. Napoleon has just been defeated and the old regime reinstated, which sucks for her painter boyfriend Cavaradossi, because he openly supported Napoleon. In the first act, Cavaradossi is painting in a cathedral. A friend of his who has just escaped jail enlists him to help his escape from the country.
The evil Scarpia, chief of police, enters and figures out that Cavaradossi has helped the fugitive escape. Scarpia's plan is to frame Cavaradossi and give him the death sentence, then tell Tosca (whom Scarpia lusts after) that the only way to ensure Cavaradossi's life is to sleep with Scarpia. In return he will have the executioners fire blank rounds at Cavaradossi at his execution and let him escape. Tosca agrees, but she kills Scarpia as soon as he has sent the "special order" to fire the blanks.
She thinks she has beaten Scarpia, and goes to tell Cavaradossi to fall down as if shot when the firing squad shoots. He does this, and she waits till the guards leave. Then she runs to Cavaradossi, but it turns out that Scarpia was lying and that Cavaradossi has really been executed. This takes place on the parapet of the famous Castel Sant Angelo in Rome. She throws herself off the tower at the end, exclaiming "Scarpia, I'll see you in Hell!"

That's the opera. This explains the scene in the church. It also explains the title partially since one of the great arias in the opera is "E Lucevan le Stelle" meaning "And the Stars were Shining". In the aria, he is about to be executed and he is recalling the first time he made love to Tosca.

I suspect it will be a play within a play type of movie, with the opera plot as the movie and life immitating art. Filmmakers love this sort of thing, where they can heavily reference a work of art that very few of the audience members will have the culture to recognize and appreciate. I can't wait to see what they do with one of my favorite operas!

Could you please tell us something more about it?

Its currently showing on Orbit in Qatar :) Its a bit of life imitating art, but it also shows how the climate of Pre-WWII Italy ( and Germany for that matter) affected the arts...and the usally electic / alternative persons who often frequent the arts.

I think there is a bit of "art and its sprit attemtping to shine through despite oppression" theme as well.

Life imitates art is the message of this movie.If you notice closely the plot and the characters resemble Puccini's opera.