Cyclical story
I just re-watched this the other night and I was struck by something I hadn't noticed before - I don't know whether anyone else has already commented on this, but I'll plough on in any case!!
At the very beginning of the film, Viridiana is approached by her Mother Superior in the cloisters of the nunnery. The Mother Superior persuades her to visit her uncle at his estate.
Half-way through the film, following her uncle's demise, Viridiana stands in the town square - this is almost exact graphic match of the earlier scene in the cloisters - trees replace stone columns. There is even the sound of a bell tolling, which is present in the cloisters scene, too. The difference is, this time, the police persuade her to return to her uncle's estate.
This got me thinking about a recurring theme in many of Bunuel's other films - that of thwarted desire, or people being trapped by forces out of their control. As much as Viridiana would like to leave her uncle's estate, never to return, she is unable to. And it is two of Bunuel's bete-noir institutions (the church and the police) that are responsible for her entrapment.