Stephen Crane was a writer who devoted many words to exposition. He told a friend that he did not trust his readers to have much imagination but felt he had to explain everything to them in detail. In this respect he was different from Ernest Hemingway, although Crane was one of the writers Hemingway most admired.
Crane devotes a great deal of explanation to Jack Potter's thoughts about how the town will react to his getting married and bringing a bride to the raw town of Yellow Sky. For example:
Of course, people in Yellow Sky married as it pleased them, in accordance with a general custom; but such was Potter's thought of his duty to his friends, or of their idea of his duty, or of an unspoken form which does not control men in these matters, that he felt he was heinous. He had committed an extraordinary crime.
Nevertheless, it is still hard for the reader to understand why there should be such a problem about the sheriff getting married. We can see that Jack Potter is an extremely important member of this community.
He knew full well that his marriage was an important thing to his town. It could only be exceeded by the burning of the new hotel.
What Potter seems to be worried about is that the citizens of Yellow Sky will take it for granted that once their sheriff is married he will become more conservative and safety-conscious, and his loyalties will be divided between the townspeople and his wife, and later his wife and children. Potter has a dangerous one-man job of protecting the town from all the uncivilized men in the Wild West. They are all represented by the character Scratchy Wilson, who is on one of his usual rampages as the train arrives. It looks as if Potter's marriage might be short-lived if he runs into Scratchy on the street with his bride. But it turns out just the opposite. The young woman dressed in her formal Eastern finery with all the buttons and bows has a spellbinding effect of Scratchy. He suddenly realizes that she has bought civilization to Yellow Sky and that there is no longer any room for people like him. Jack Potter and the town's citizens don't have to worry about their sheriff's marriage having an adverse upon his effectiveness as a peace-keeper. He will be twice as effective as a peace-keeper now that he is a married man. The whole town is destined to be transformed.
The moral of Stephen Crane's story is that it was the good women who tamed the Wild West. They insisted on law and order. They wanted schools and churches and safety and proper manners--and they got everything they wanted through some magical spiritual power of righteous womanhood and motherhood.