Much has been written about the role of the environment in this film. Rarely can natural (and outwardly naturalistic) settings have been so crucial to the action and ambiance of a movie. Manhattan springs to mind as another work in which the setting functions almost a key character (bet you didn't expect to see a comparison with Woody Allen in this review).
The director forces the audience to see something explicitly religious (and in the case of the guy, Christ-like) in the two leads, by depicting overt religious symbolism in their actions and gestures. There is nothing simplistic in this portrayal, however: the characters' actions are always underpinned by a faint whiff of shamanism, nature-worship or even downright satanism, bringing a delicious - and potentially controversial - complexity to the film.
The action appears to take place outside the modern world, or at the very least parallel with it (I referred to the "medieval" atmosphere evoked by Dumont's work in another review, and Hors Satan is a little like that too). In this strange parallel world, the police, for example, don't act as expected - in fact, nobody acts as expected. Despite the slow pace, however, I never got the feeling that the story was not moving forward (and I'm baffled by the failure of one reviewer to identify any storyline at all).
Much of the tension lies in the audience's fear - of what the characters will do to one another and to the landscape, of what the consequences of their actions may or may not be, and of what the movie's ultimate outcome will be. It is this elemental drama that drives the film forward - in a slow-burn movie in which death accounts for an amazingly high proportion of the "action" that actually does take place, life and death are in the balance in an extremely immediate and terrifying way. The central Christ-like character can be violent, and his actions incomprehensible, perhaps reminding us that Christ was himself capable of unexpected violence (for example when throwing the money-lenders out of the temple). Although of course the director also leads us towards a view of the lead character as a Satanic figure, particularly in one almost unwatchably horrible scene.
Perhaps the central achievement of this film - by an apparently atheist director, remember - is to have created a powerful drama with a complex Christ-like figure who reflects the mysticality and profound unknowability and yet the intangible magnetism of the original biblical Christ, while incorporating elements of the satanic into the character too. A difficult comparison for Christians to swallow, though.
