The Selection
The Selection symbolizes the way communities seem to involve themselves in the love lives of young people. For Eadlyn that is unignorable and pressing. The Selection reduces her will substantially, making her subject to a social program that she resents. Also, in a broader sense, the Selection symbolizes the sacrifices of mating, because she must submit herself to a marriage which constitutes a sacrifice of freedom.
The jealousy motif
Throughout the social dance of securing a worthy mate, the various characters in the Selection become increasingly self-aware, leading to a motif of jealousy. Jealousy seems to represent the self-esteem issues of youth and the way that romance accelerates those feelings and brings them to a peak. Jealousy is a dilemma that comes when a character, like Camille or Baden for example, projects their self-esteem issues onto a social situation over which they have no control. It is a desire for social power.
Erik as a symbol
Erik is the opposite of the garish, showy men who attempt Eadlyn's attention. He is shy and passive, and something about him is interesting to her. Erik is a friend who might have a shot with Eadlyn, but he isn't brave enough go for it with such low self-esteem. In her life, he symbolizes a kind of failure. She might love him, but she can't make him pursue her; he subtly betrays her by being too deferent and passive.
The heart attack
When Eadlyn finds out that her mother has had a heart attack, that changes her in some ways. It makes her confront the likelihood of death, and it shows her the cycle of life. Her mother used to be a single gal like her, but then sacrificed to create her and the family. She is more willing to do the same sacrifices because of the heart attack, because the heart attack shows her the truth about human life—that it is short and that it requires sacrifice.
Social caste instability
The disorder of Eadlyn's community is worsened by the recent overhaul of the caste system, but that leaves her with a pretty unstable situation. She doesn't want to participate in the Selection, but because she feels she can quell the instability, she accepts. That acceptance is a kind of responsibility she assumes. She sacrifices her own volition to do what she thinks is best for the stability of her town. She accepts responsibility for stabilizing the city she leads.