Love
The most obvious theme in A River Sutra is that of love. The Narmada River itself is described as a lover, flowing to meet her bridegroom, the Lord of the Oceans. In each story that the nameless narrator hears he learns more about what his friend Tariq Mia calls the secrets of the human heart. The varieties of love that touch the heart are as endless as the stories of the Narmada River. The narrator learns of a monk's love for all living creatures. Trying to live by the doctrine of "ahimsa" or nonviolence, this Jain monk tries to empathize with the suffering of everything from the smallest insect to his own wealthy father. In attempting to utterly deny his own feelings and to take on the pain of the world, the Jain monk finds that his frozen heart has melted. Master Mohan falls in love with a blind boy singer through the purity of the boy's voice. In caring for this boy, Master Mohan is selfless. Acting as a true father, Master Mohan forgets his own needs, putting the boy's happiness above all things. When the boy is murdered, it seems logical for Master Mohan to take his own life. So too does the courtesan's daughter commit suicide after her lover dies. Some love, the narrative suggests, is so all encompassing that life without that love becomes impossible to bear. Other manifestations of love, however, offer sustenance for continuing to live and persevere. The love that the ascetic Naga Baba feels for his ward Uma helps him to decide to rejoin the world and abandon his ascetic ways. Once Nitin Bose has recovered from the insanity brought on by his strange desire for a mystery woman and his renunciation of that desire, he is free also to rejoin the modern world. The narrator himself seems to have never searched for his own capacity to love. A bystander, he seems only able to listen to the stories and watch the Narmada River flow past.

Renunciation
As the narrative begins, the reader learns that the narrator has decided to renounce the modern world. Deciding not to pursue promotion within the bureaucracy for which he works, the narrator chooses instead to become the caretaker of a government rest house. Renunciation is a major tenet of the religions of India, and thus a major theme of the novel. The narrator admits that his renunciation of the world is minor compared to the true "vanaprasthi," those who have "retired to the forest to reflect." As he explains, "I knew I was simply not equipped to wander into the jungle and become a forest hermit, surviving on fruit and roots." But this is exactly what many of the people he meets have decided to do. The Jain monk was a fabulously wealthy man, the son of a diamond merchant, and yet he renounced this lifestyle to search for enlightenment. The Naga Baba was a renowned archaeologist who chose to dress in rags and wash in the ashes of the cremated. Both of these men in choosing the humiliations and hardships the world has to offer are a bit incomprehensible to the narrator. Mehta does not judge these ascetics harshly, but the narrative suggests that true enlightenment comes from love. And to truly love, one must connect with the world. The Naga Baba's eventual path, rejoining the world as Professor Shankar, seems perhaps a better destiny than the one most likely to befall the Jain monk. The narrator imagines that one day he will see the monk's emaciated corpse floating down the Narmada River. To reach his enlightenment, the monk will neglect his body's needs and potentially will starve to death.

Isolation
Closely related to the theme of renunciation is isolation. However, the truly isolated in the novel have not chosen their fate as the Jain monk and the Naga Baba did. The musician, for instance, is isolated by her ugliness. Her face repels possible suitors, and the man she loves abandons her. Forced to be alone, her fate is especially difficult. As a female musician she learned to be "the bride of music," her delicate chords are meant to complement the more masculine sounds of a male musician. Having found the perfect harmony with her fiance, she cannot imagine being able to play with anyone else. Her plaintiff sounds remind her of what she has lost, so she gives up her music. Similarly, the courtesan is isolated when her art no longer has meaning in the modern world. Trained in the "art of love," the courtesan dreams of a world long since past where she was able to perform before appreciative audiences. Changing times have changed her into a prostitute, forced to have sex with vulgar men. She lives without hope that the former world will ever return. Isolated from love and happiness by circumstance, these women do not have the power to renounce the world. It has renounced them.