Johnny, the dud
Johnny represents a kind of weakness, but it isn't physical weakness (although he is physically weak). Johnny represents the lack of ethical resolve. If he had a stronger commitment to becoming the best man he could be, then he obviously would not have resorted to drinking away his money stress with his last remaining money.
The fact that Johnny never sees past his own misery to truly appreciate his wife and his children, and the additional suffering he causes them, it means that Johnny is a symbol for a failure. He represents the bad kind of person, the kind of person who doesn't sacrifice for those they love, like Katie does the whole book through.
Sergeant savior
When the change of fortune comes in the novel's final chapters, there is a man called Sergeant McShane who marries Katie, supporting the family, allowing her to quit her difficult job as a janitor, and allowing for her children to go to college. Helping support the kids was the one thing that Johnny never did, so already, this almost-stranger is a better giver of love than Johnny, not because of his money, which is convenient, sure, but because of his willingness to care about the children, something Johnny could never seem to do.
Sergeant McShane represents the re-introduction of order to the difficult and strained lives of Katie, Neeley, and Francie (especially after the sudden drinking death of Johnny). He represents a chance at a second life, making him what literary critics have sometimes called "a messiah character" because he offers the same things as Jesus does in Christian tradition: redemption, love, support, and most importantly, a chance a second shot at life.
The racist school
When little sweet, Irish, Francie goes to school, she can't conceive of what would possibly make everyone so mean all the time. The sad truth is that the reader knows about racism, which the character in the book seems not to understand yet. In Brooklyn, Irish people were often mistreated, treated with severe hatred and bigotry, but as a child in an Irish community, Francie might not have known that. When she gets to go to a new school, the idea is that racism has not rattled the middle class as it has the lower class. This is all clearly significant to an adult like Katie and Johnny, but to Francie, it's all new and confusing.
The heartbroken Francie
When at the end of the novel, Francie gets left brokenhearted by a soldier who was leading her on, the symbolism might remind the reader of Katie being disappointed by Johnny before finding a good man. In other words, the implication is that Francie will be able to find a new, better life for herself, but not by having the man she wants. After all, following her eyes is what got Katie into a marriage with Johnny before she knew his integrity and character.
The pedophile
The pedophile incident is unfortunate but significant for Francie. In that moment, she learned (albeit from tragedy and trauma) that life is much harder for women than men when it comes to sexual safety. Luckily for Francie, her mother was there to save the day. How did she do it? She pulled out a gun and shot the man to death right in front of the little girl. This is a helpful picture of justice, but it is undoubtably a loss of innocence for Frankie who learns that the world is harmful sometimes, and that in order to protect her from evil, her mother needed to resort to that violence. In a word, the incident teaches Francie about the toughness of her mother, as if to say, "You're gonna need some grit to survive."
