Themes of The Betrothed include greed, forgiveness, and the benefits of innocence and humility.

Greed is a major theme in The Betrothed. Don Rodrigo is a selfish man who wants to have Lucia as his mistress while he's still a virgin simply to win a bet. He's willing to go to great lengths to have her; he puts his life on hold as he pursues her, going so far as to track her down when she flees from him. Other characters fall prey to greed as well. When Lorenzo is separated from Lucia, his despair sends him into a tavern where he gets so drunk that he admits to inciting a riot and is imprisoned and banished. His greed in drinking to excess creates problems for him throughout the novel.

The benefits of innocence and humility is another theme in the novel. Lucia is largely saved by her innocent character and kindness. It makes people want to stand up for her and help her. It's one of the things that makes Don Rodrigo want her as well, though, so it's not always a positive thing. However, Lucia is about to make her way through a series of benefactors and protectors simply because she is kind and innocent. If she was cruel or reckless, it's likely that people wouldn't have offered her the kind of assistance they did and she would have ended up being ruined by Don Rodrigo.

Forgiveness is another theme in the novel. It's perhaps best exemplified by Fra Cristoforo, who once killed a man. He was wealthy, privileged, and gave it all up to repent for his sins. In doing so, he found forgiveness. In this position, he's able to give shelter to others who seek it—like Lucia, when she arrives trying to get away from Don Rodrigo. Because Cristoforo was able to be forgiven, he's grown into a kind and saintly man who has a lot to offer the world. The message is that if people were given up on as soon as they committed a sin, no one would be left to offer assistance to those who need it.