Forgiveness
The entire story hinges around the theme of forgiveness. We begin with three inmates escaping from prison. Two of the three, Delmar and Pete, walk towards a baptism while on the run from the law. They seek forgiveness of their sins from God, thinking that it will clear their record with the law. While Everett does not seek to be baptized, he also wants forgiveness, but from his ex-wife, Penny. Then later, Everett must ask for forgiveness from his two friends for lying to them about a treasure that doesn’t exist. When the men play as the Soggy Bottom Boys at the campaign dinner, Pappy O'Daniel pardons them and forgives them for their sins on the grounds of their excellent music-making. Then, right before the lawmen try to hang the men outside Everett's cabin, Everett prays to God and asks for forgiveness, which comes in the form of a giant flood which saves them.
Dual Nature of Man
Towards the end of the film, Everett reveals that he has lied to Pete and Delmar: there is no treasure. Everett selfishly created a story in order to convince them to escape with him. Even though he clearly cares about the wellbeing of his friends, he hardly apologizes to them and proves himself to be a rather selfish character. Thus, Everett is a man with an alternately warm and selfish personality.
Many people in the film exhibit many shades of their personality. Big Dan seems like a very friendly man until he is beating Everett and Delmar with a branch. "Baby Face" Nelson is alternately joyful, maniacally self-impressed, and depressive. Pappy O'Daniel, the governor of Mississippi, also exhibits this duality. When he and The Soggy Bottom Boys first cross paths at the recording studio, he wants nothing to do with them. Yet when he discovers that his constituents love them and their music he becomes their best friend, even granting their pardons in order to win votes for re-election.
Music
While the concept of music is not discussed much in the film, it plays an important role not only in the aesthetic of the film, but also in the plot itself. When Everett, Delmar, and Pete encounter Tommy, the gifted guitarist who sold his soul to the devil, the men walk into a recording studio and record a perfect rendition of "Man of Constant Sorrow," which then plays on the radio for the next few days and launches them into widespread popularity. This popularity is what redeems them in the end, when they play their songs at Homer Stokes' campaign dinner. People love their music with a passion that overrides their politics. When Homer Stokes tries to silence their singing, he falls from grace. It is the power of music that earns the Soggy Bottom Boys their redemption, allowing Everett to achieve his goal of winning back his ex-wife, Penny.
Politics
Politics are in the background of the protagonists' journey throughout the film. First, they encounter Pappy O'Daniel outside the recording studio and attempt to make conversation with him, but he wants nothing to do with it. Pappy is a frustrated and easily-angered man, harried by the fact that it looks like he might not win reelection in Mississippi due to the growing popularity of Reform candidate and champion of the common man, Homer Stokes. Homer Stokes advocates for the overlooked farmer, and proudly leads a chapter of the Ku Klux Klan. At his campaign dinner, he offends his voting base by speaking out against the Soggy Bottom Boys and disapproving of their racially integrated band. His insulting of the popular bluegrass group is enough to lose Stokes his support. After Stokes is dragged out, Pappy O'Daniel takes to the stage and pretends to be the Soggy Bottom Boys' biggest fan, which wins him favor with voters. Politics is depicted as a quick and dirty game in the film, responding to the winds of public opinion more than principle.
Adventure
The whole film is an adventure story, a tale of a journey of three men towards a distant treasure. After all, it's based on one of the most iconic adventure epics in history, Homer's Odyssey. The film follows the escaped convicts as they travel through various locations and escape almost constant dangers. Some of the trials along the way seem touched by magic, and the boys must navigate unpredictable scenarios and characters. The spirit of adventure keeps the men moving forward, working towards a treasure that they can never seem to find. Even when they reach the end of their journey, more adventures and trials await.
Science and Reason
Everett positions himself as a rational thinker throughout the film, not easily convinced by vague spiritual ideas. Indeed, while Pete and Delmar get baptized and engage in more magical thinking throughout, Everett believes that there is a rational explanation for everything. In the beginning, the blind prophet tells the men's fortune, and while Delmar and Pete are wont to believe it, Everett dismisses it as illogical. Even when they are conveniently washed away by the flood, just after Everett prays to a God he claimed not to have believed in, Everett will not admit that there are some mysterious and divine forces at work in their favor. Instead, he has yet another explanation for the flood: "Well, any human being will cast about in a moment of stress. No, the fact is, they're flooding this valley so they can hydroelectric up the whole durn state. Yes, sir, the South is gonna change. Everything's gonna be put on electricity and run on a paying basis. Out with the old spiritual mumbo jumbo, the superstitions, and the backward ways. We're gonna see a brave new world where they run everybody a wire and hook us all up to a grid. Yes, sir, a veritable age of reason. Like the one they had in France. Not a moment too soon."
Religion
The film examines the theme of religion rather ambivalently. When we first see evidence of the Southern church, it is the striking image of dozens of white-robed individuals wandering through the trees towards the water to be baptized. They sing together as they walk towards the river, and Delmar and Pete are in awe of the spectacle. Delmar desperately wants to be forgiven by God for his crimes on Earth, but Everett must remind him that redemption under God is not the same thing as redemption under the law.
Later, when they are about to be hanged outside Everett's cabin, Everett, rather uncharacteristically, prays to God for guidance and help. Just as he prays, a giant flood comes and washes them all away, preventing their hanging. Everett still has a rational explanation for the flood once he emerges from the water, but its perfect timing and scale suggest a divine hand. O Brother, Where Art Thou? doesn't quite take a position on the existence of God; it leaves the question open. The film is itself a kind of parable.
