Babylon was an ancient city on the Euphrates River in Mesopotamia. The Biblical Book of Genesis translates Babylon as meaning "confusion." In addition, Babylon became a city occupied by various peoples, among them the Persians and Muslims. Thus, the confusion and mixture of peoples and cultures is appropriate to Fitzgerald's story about pre-crash Paris, inhabited by wealthy and dissolute expatriates.

With this history of Babylon in mind, the themes of Memory and Atonement for the Past are, indeed, appropriate. Charlie Wales is much like the inhabitants of Babylon:  he is a wanderer, who now lives in Prague; at the home of Marion and Lincoln Peters, he is actually an interloper as Marion does not want him there.

• The Power of Memory

Charlie feels much guilt over his dissipated past and hedonistic behavior as he drank excessively and wasted money on frivolous matters and acted immaturely. His actions that led to the death of his wife Helen haunt his memory, especially after his visit to the Peters's home,

Going over it again brought Helen nearer, and in the white, soft light that steals upon half sleep...he found himself talking to her again....

Charlie's efforts to push back the past and reclaim his honor and his daughter Honoria are also haunted by memory as his dissolute friends of old, Lorraine Quarrles and Duncan Schaeffer, appear outside the Peters' apartment. 

•  Making Atonement for the Past

Having reduced his libation to one drink a day, Charlie works to earn the respectability he needs in order to regain custody of his beloved daughter Honoria. When he has his daughter with him at a restaurant, Charlie ponders the importance of character:

He thought he knew what to do for her.  He believed in character...He wanted to trust in character again as the eternally valuable element. Everything else wore out.

Unfortunately, the past haunts him from the Ritz and his former friends. In the end, after Marion makes him wait more time in punishment for his past acts, Charlie sits in the haunted Ritz and ruminates,

He would come back someday; they couldn't make him pay forever. But he wanted his child, and nothing was much good now, beside that fact. He wasn't young any more....

Charlie's concern over time prevails throughout his thoughts as he is haunted by his past and his anxieties about the future.