I think one element that comes out strongly in this tale is the sense of being unable to escape our past. Charlie has worked hard to reform himself and has tried to move away from his heady, decadent and hedonistic days in Paris. He returns to the symbolically entitled "Babylon," but he finds that his past is still there to haunt him, and in the end prevents him from gaining what he has come to recover - his daughter. The story makes us ask some hard questions about our ability to move on and not let our past mistakes hinder our present lives.
In "Babylon Revisited," there is also another theme that prevails throughout the novel: Guilt vs. Innocence.
Charlie Wales returns to Paris to prove to his sister-in-law that he is no longer guilty of dissipation and neglect. He strives to prove to the sister-in-law that he is no longer guilty, and that he has turned his life around by avoiding heavy drinking, and by not squandering his money as he did before the Crash. He desires to show how he will raise Honoria if allowed to take her with him.
There are several themes intertwined that are closely related. Change and transformation are certainly involved in this story of a recovering alcoholic who is desperate to get his daughter back from his dead wife's sister and her husband. But there is also guilt, and money at the heart of the story.
Charles is dealing with several crises at one time, the death of his wife, his guilt and feelings of responsibility for her death, the loss of his financial stability due to the crash of 1929. He is also mourning his lost life, the life he had before the crash, the irresponsible, wild life of drinking, not worrying about tomorrow. He actually feels guilty about how much money he was able to make during the stock market boom.
Charlie struggles with his conscience over Helen's death. They had argued about her behavior, her kissing another man in front of him, flaunting her ability to make him jealous. He went home and locked her out of the apartment. Helen walked all the way to her sister's house in a driving snowstorm, soaking her to the skin. Helen dies as a result of heart trouble, not pneumonia.
Charlie also has to resist the temptation to return to his old life, his friends are still drinking and partying, buy he must remain sober so that he can satisfy the court's requirement for him to get Honoria back from Marion Peters, her legal guardian.