This film, introduced by BFI Programmer-at-large Geoff Andrew, is part of the cinema's Big Screen Classics season (details here).
Chicago Reader review:
Eric Rohmer's droll and delicate comedy of language (1969), about a devout Catholic (Jean-Louis Trintignant) who delivers an all-night monologue on the philosophy of Pascal to escape being seduced by the lovely atheist Maud (Francoise Fabian). Number three in Rohmer's series of “Six Moral Tales,” it is probably the most pure: the plotline transpires entirely in the central character's mind and is never explicitly acknowledged by Rohmer's direction, which concentrates instead on the elaborate gambits of a style of speech meant to do anything but communicate.
Here (and above) is the trailer.