Subtext Behind Train

That can certainly be part of the narrative, but I find films always have an often subtle subtext.

Consider the following:

The train represents the world, and the people in it, humanity. Outside the walls of the train is a different, unrecognizable world. It is cold and barren, a symbol of the empty real world, where survival is impossible. Notice how those living in the tail end of the train, have no windows. They cannot see the old world. This is alluding to the fact that those on top (front of the train, representing the bourgeois), filter the prism of information that comes to those beneath (those in the back of the train, representing the proletariat). Curtis, our protagonist, foments a plan to pierce towards the front of the train to find its creator, Wilford (ruling class; elite). Mason enforces Wilford's law. This alludes to the belief that Freemasons rule the world. This is further reinforced by her use of the phrase "so it is." This is a ritual phrase said to be used by Freemasons, similar to saying "amen" at the end of prayer.

The film happens during New Year's Eve. The scene with the fish symbolizes the transition from the Age of the Fish (representing Christianity), to the Age of Aquarius (representing the synthesis of intellectual knowledge with the dissolution of religion). The reference to water is symbolic of this distinction. The class struggle on the train is symbolic of civil war, occurring before a new paradigm is established ("74% of you must die"). Their plight, then, is the plight to obtain control over water, which will inevitably allow them to control the world (triumph of Aquarius).

Curtis eventually reaches Wilford, where he learns that what he thought was reality, is false (alluding to artificial knowledge thresholds placed on the lower classes). Those in the back of the train (society writ large), by virtue of their poor living conditions, are unable to self-actualize and escape the confines of their existential prison.