Here is a thought (not mine, although this sounds good).
Though Buñuel never states what the symbolism represents, leaving it to the viewer's understanding, one critic, Roger Ebert, wrote a lengthy interpretation of the film's symbolism, which includes the following paragraph: "The dinner guests represent the ruling class in Franco's Spain. Having set a banquet table for themselves by defeating the workers in the Spanish Civil War, they sit down for a feast, only to find it never ends. They're trapped in their own bourgeois cul-de-sac. Increasingly resentful at being shut off from the world outside, they grow mean and restless; their worst tendencies are revealed."