The third and final act is set on Bernarda's patio, a room of "four white walls, lightly washed in blue." At the top, Bernarda and the daughters eat together around an oil lamp while La Poncia serves them and Prudencia, a visiting friend of the matriarch, sits apart. The curtain rises on an extended silence.
After a bit, Prudencia announces she must leave but Bernarda convinces her to stay. Bernarda asks her about her husband; Prudencia shares that he will not speak to their daughter, even though the daughter's absence is painful to Prudencia. Bernarda approves of the husband's activity, calling him a "real man" and stressing that a "disobedient" daughter "becomes an enemy." Prudencia says she takes solace in the church.
Suddenly, there is a banging against the walls, which Bernarda explains is a stallion that is locked in a stall and kicking to escape. Bernarda orders the stallion to be taken out in the yard with a tether around its neck, to prepare to be mated with the mares the next day. Under her breath, La Poncia laments that Bernarda has the best herd in the area but that prices are too low.
Adela stands to leave, saying she wants water, but her mother demands she sit and then calls for a pitcher to be brought. Prudencia asks about Angustias's impending marriage, and Bernarda says that it should happen within three days. Amelia and Magdalena fight over the latter having spilled salt. Angustias shows Prudencia the ring, and though it is admired, Adela insists it ought to be a diamond instead of pearls. Prudencia adds that in her day, "pearls signified tears." Bernarda changes the subject, and they talk about her furniture, which is quite lovely and expensive.
Prudencia leaves when the bell of the last church call rings, and they all wish her well. Having finished dinner, Adela says she will head out for a stroll, and Amelia and Martirio insist they will accompany her, to her chagrin. Magdalena leans against the wall as they leave.
Once they're gone, Bernarda confronts Angustias and demands she forgive Martirio for the photo robbery so that the family can have "harmony." As Magdalena drifts off to sleep, she adds to Angustias, "you'll be gone in no time." Bernarda asks Angustias what time she and Pepe finished talking the night before, and Angustias says 12:30. The mother wishes to know what they discussed, and the daughter suggests it seems as if his mind is always elsewhere, a problem Bernarda suggests she learn to ignore if she wants to get along with a man. When Angustias confesses she is worried he is hiding secrets from her, Bernarda redoubles her efforts to convince the daughter to allow secrets and not to pry.
The girls reenter, discussing how dark the night is. Adela notes how the white stallion filled the dark, and Amelia says it was frightening. Angustias heads to bed, sharing with the others that Pepe is not coming this night. Adela asks Bernarda about a certain poem that is often spoken when a star falls, and Bernarda shares that there are many secrets of "the old people" that are forgotten. While Amelia says she tries not to look at such things, Adela says that she wants to spend the night outside. They all bicker a bit as everyone but Bernarda leaves for bed.
La Poncia enters and Bernarda immediately picks a fight, sarcastically pointing out that the "very grave thing" doesn't seem to be happening. La Poncia tries to diffuse the situation, but when Bernarda presses it, La Poncia reminds her she can never keep watch in a person's heart. As the maid tries to insist she will stay quiet and keep her place, Bernarda snidely asks whether she has any more lies about Pepe staying late, and La Poncia reminds her that even if all is well, tragedy can strike at a moment's notice.
A servant comes in to tell Bernarda all is clean, and the matriarch heads to bed. La Poncia laments that Bernarda is blind, but notes that sometimes it's easier to be blind when you lack control. The servant agrees. La Poncia notes that Adela could have controlled herself and not have led Pepe on, and the servant shares that many gossips suggest he did not have to try very hard at all to seduce her. They discuss how Martirio would destroy the world rather than let someone else have Pepe, and then Adela enters, claiming she wants water. She asks why they are not asleep yet and then leaves.
The servants confess their fatigue and leave. A moment later, Maria Josefa enters, holding a lamb in her arms. She sings a song about how she and the lamb will head off to the sea and leave behind "Bernarda, old leopard-face" and "Magdalena, hyena-face." She sings until she walks out.
Act II ended with heightened dramatic irony and a suggestion of Adela's pregnancy, but Act III does not move the story forward. Instead, it is concerned with continuing to explore the tragedy of sexual repression and individuality.
The sexual repression is as clear as ever. The stallion is a perfect symbol of the way Bernarda attempts to control her world. Though the horse thrusts aggressively against its confines, Bernarda only addresses the problem by allowing the horse minimal rein in the field. Similarly, Bernarda is blind to the extent to which her daughters are thrusting against their confines. They are all desperately unhappy and yet she persists in keeping them on a short leash. The "harmony" that Bernarda insists Angustias try to keep only comes at the cost of such intense oppression, which means that "harmony" is unnatural and requires strictures. The most damning indication of the cost of sexual repression is that it engenders the same attitudes in those who ought to oppose it. When Adela wants to take a stroll, both Martirio and Amelia insist they will go with her – in effect, they are willing to reproduce Bernarda's spying attitude, even though in a perfect world they ought to realize that such an attitude is what keeps them repressed.
Bernarda's attitude towards men, specifically that they ought to be allowed to do as they please while women enable such freedom, are on full display. She commends Prudencia's husband for refusing to confront his brothers, even though the man's refusal comes at the cost of family. Further, Bernarda's insistence to Angustias that the latter must ignore her husband's potential indiscretions is sad, but it implies the truth, which is that women have no control in their world. A woman, in order to be happy, has to accept a certain amount of repression. Though Bernarda is praised by Prudencia for having the strength of "a man," the cost of such strength is that Bernarda has to accept her place. Perhaps this helps explain the vicious circle of repression that Bernarda engenders.
Adela maintains her place as the tragic figure in the way she insists on flaunting her true independence and individuality. She is the closest to the symbolic stallion and as such finds it beautiful whereas Amelia finds it scary. The uncertainty of the dark scares everyone except Adela, who finds in the uncertainty of life an exciting prospect. Adela reveals herself as something of a poet here, especially when she speaks effusively of the beauty of a falling star and how she likes to look right at it.
The other character who expresses a desire to be free in this section is Maria Josefa, who sings alone of her escape from repression. She carries a lamb, a traditional symbol of innocence, and sings about going to the sea, which she equated with being married in Act I. There is something sweet about the way Maria Josefa equates innocence with freedom (and by extension sexuality, since the sea was linked to marriage earlier). It again stresses Lorca's point that the natural state of humankind is our desires, and that for all their complexity, they are also simple and innocent.
This section also provides some indication of Lorca's fascination with death. What Prudencia says about the pearls reveals Lorca's sense that happiness and sadness are intertwined, and by extension life and death are intertwined. Prudencia shares that pearls signify tears, even though they are obviously meant to decorate. In the same way that beauty leads to tears, so does life lead to death. Magdalena is the one who sees death coming. When she tells Angustias that she will be gone soon, both Angustias and Bernarda assume she means gone to marriage, but Magdalena likely means it in a more existential sense, that they will all die soon enough and their problems prove meaningless.
In terms of class, we see how Bernarda is unable to understand the forces in her life outside of their monetary value. The stallion represents unbridled sexual passion, but Bernarda sees in that energy something that needs to be controlled so that she can produce a good set of horses to sell. Similarly, there is much talk with Prudencia about the wealth Bernarda has amassed, suggesting that Bernarda refuses to consider the unbridled spirit of humanity while she has her eyes turned too fully to the material world.
Though not a huge part of the act, Lorca's perspective on religion is also apparent here. Prudencia admits she turns to the church in order to find peace in having repudiated her daughter, something she does only because her husband insists upon it. This suggests that the church is meant to help us accept the unhappiness in our lives rather than bringing happiness directly. However, Prudencia worries that she will soon have to quit the church because her blindness will be mocked, which shows that the church cannot transcend the gossipy and base nature of humans.
Lorca continues to insist on precise theatricality. The opening of the act is creepy and evocative, with silence on stage as the woman are lit simply by an oil lamp. The white walls are now a light blue, suggesting something is changing, that Bernarda's attempt to keep a 'clean' house are no longer going to be as successful as she'd like, but their greatest effect would be one of visceral unease as the whiteness to which the audience has grown accustomed is now compromised. Lastly, Maria Josefa's song is a highly theatrical device.