Normally I really hate it when a piece of great 'classical' music is used on a film soundtrack, and for a whole lot of reasons. Herzog and John Boorman have ruined most of their films for this reason. Think of 'Nosferatu' and 'Excalibur'. If you don't know the music you are lucky and it might not be so bad but even then, if you are good with music, you should notice there is something wrong.
This film, however, manages to pull it off triumphantly. No other piece of specially written music could have worked so well as Mendelsohn's Violin Concerto does. The result is one of the most unforgettable, beautiful, lyrical sex scenes I have ever seen. It explodes onto the screen in sound and images that are as near to ecstatic as seems possible. It even provides a valuable insight into the concerto. The violin is well enough recorded for the time , so full and strong, that it is possible to internalise it in a surprising way. And it is perhaps surprising in itself that the violin can so well represent sexual ecstasy - but high frequency sound is something this scene shares in common with the justly famous airoplane sex scene in 'Emmanuelle 1'.
When I say 'beautiful' and 'lyrical' don't imagine that it is not essentially and strongly erotic because that of course is the whole point. There are plenty of Hollywood sex scenes trying to be lyrical and beautiful but they miss the mark and end up with something that is just kitsch and sexually dishonest. And that sort of thing is so common because it is so easy to do. A scene like this needs to be disturbing and surprising in some way for it to be of real value. See my reviews of comparable scenes in other films such as 'The Postman Always Rings Twice'.
And again, lyrical it may be but smooth and polished this scene is not. It is filmed with unstable hand held camera (this is an early 70's film before steadycam) and the effect of lyricism is produced by the beauty of the girl's body itself and its movement, and of course the intense lyricism of the violin. The camerawork itself has all the fumbling, jerky quality that passionate first-time sex has so often in real life.
The story is based on a classic Polish realist novel about a girl from a respectable family fallen on hard times who falls in love with a lodger and has a baby by him and without him being aware of what has happened as a result of having moved to another city. She has the baby suddenly and alone and disposes of it straight away. This is the 'sin' which sends her on a downward spiral into the criminal underworld in a typical late 19thc manner. The film has a convincing realist look throughout despite or perhaps because of various references to contemporary schools of painting. As always Boro likes to observe the texture and surfaces of things like such painters.
But what is in the end important about the film is the element of transcendance that is occasionally present through the music I have mentioned or through the beauty of some of the visual images and the girl herself.