I was inspired to write this, my first film commentary ever, when I was reading through those already posted. It struck me that nobody seemed to have got who "the girl" (played by Polanski's wife Emmanuelle Seigner) is! Everybody who mentions her -- and most do -- say she's in the film for no reason, she keeps appearing and disappearing to no effect, she's never explained, and that the film would've been much better if Polanski had only left her on the cutting room floor.
I hope Polanski is getting a kick out of this: the fact that nobody has got the secret of this, his most recent (and I think brilliant) film. I hope he's reached the point in his life and career where he cares more about making the art he had in mind than he does about whether people are getting it.
Darlings, "the girl" IS Lucifer!! It's right out there in plain view. And this is the beautiful irony of this movie: that s(he) IS right out there in plain view, to all these people who are seeking her, and doing all this stuff to summon her, and she's right there -- which is one of the oft-told truths about gods and deities throughout time, that they're right there, right next door to you, and you don't even notice them. This is the truth (one of them) that Polanski is putting on screen here. Witness the scene in the St. Martin Chateau where "the girl" crosses paths with Mrs. Telfer; look at the expression on the girl's face; it is ironic and absolutely amused. And there are more "clues" -- many more.
The girl is the only person in the film with actual supernatural powers. She floats. She is always around whenever Lucifer is being discussed. Although she repeatedly rescues Corso, she has anything but an angelic face. Her beautiful face has a subtext of evil and corruption. She anoints Corso with her blood in an arcane symbol on his forehead! And -- the giveaway -- when she finally has sex with him, didn't you notice that her eyes turn into demon eyes? that she morphs into a devil?
This is really a love story. It is about Lucifer finding a mate -- the person s(he) will accept to enter through the Ninth Gate into his/her kingdom. You can see how "the girl" is evaluating all the candidates throughout the film and how s(he) decides on Corso who is, after all, corrupt from the very beginning and therefore a likely candidate. Witness the scene when Corso is beating Pablo to death, pounding him repeatedly on the face. "The girl" says "Well, Mr. Corso, I didn't know you had it in you." She is obviously pleased with him; she is choosing her mate!!!! The reason she keeps rescuing him is because he is the one she's seriously considering.
Watch the film again. See if I'm not right.
Anyway, what probably has Polanski laughing is the fact that he managed to disguise all this so brilliantly simply by making Lucifer a girl. He's probably a bit surprised by how completely this simple gender-switch had the audience totally fooled! If "the girl" had been "the boy" -- an equally beautiful young man who follows Corso throughout the film -- I'm sure half the audience would've gotten it. But nobody, still, can imagine that the mythic figure of the devil could be female. But of course! The gods are androgynous; they have to be!
And Polanski adds yet another layer of irony and humor by dressing "the girl" as a student with different color socks: the most innocent, innocuous, universal and asexual dress imaginable. Put yourself in Lucifer's shoes. Isn't this how you'd disguise yourself, if you were making a visit to earth? Obviously it is because, if the people who saw this movie are any sample, nobody would suspect.