From looking just at the characters and their motivations, you get a clear sense of the importance of money and the drive to insure a steady income for Polly, and particularly in the case of Mrs. Mooney, for her daughter. She, in fact, is one of the strongest indicators in the story for the various mores and customs of the time as she manipulates nearly all of them in order to accomplish her goal of getting Polly married to one of the men in her boarding house, particularly one of the dependable ones with a stable job.
The power of the church, particularly in matters moral is laid out and shown by the way it drives Doran to feel that he really ought to marry Polly despite his misgivings. The social mores of the time of course are also demonstrated by the way that Polly seduces Doran and then the pressure that can then be brought to bear on him to marry her because of their tryst.
In that society marriage is more about social standards, public perceptions and formal sanctions than mere feelings. Mooneys belong to a lower class (Mrs Mooney is a butcher's daughter and married to father's foreman) So Mrs. Mooney's intention is to make some prosperous man marry her unfavourable child. Poor Mr. Doran becomes the victim. Doran realizes how his family would react to this marriage. For Mooneys this marriage is a profit (Mrs. Mooney make sure Doran has a steady job, salary and savings and he's form a higher class) whereas for Doran it's an entrapment. Maariage has commercialized in that society.
Joyce slaps at some extremities in the religion, prevailed in that society. Union of a female and a male was considered 'a sin'. The priest magnified it to greater extent. People were stereo-typed in that society (Dublin is a city where everyone knows everyone else's business)Doran had two options, whether to marry Polly or to run away, but he feared the latter since it's going to destroy his sound reputation.Mrs. Mooney, unlike other mothers, demanded marriage (not money as a compensation) or to risk public disclosure. So those religious and social forces trapped this man, who was not in the need o initiate a relationship with Polly. He hd to wedPolly despite of her vulgerity, wrong grammer, unfavourablefamily and social class. What mattered to the pople most was reputtion. Joyce evidently provides impressions about early 20th social customs plus the pathotic lives of dubliners.