Mahanagar is a subtle assertion of Ray's belief in the emancipation of women. Arati represents the emerging liberated middle class woman who breaks class and gender stereotypes to help her husband financially.
Much family opposition does little to deter her from her decision and her success in her job only instills more confidence in her.
Her husband initially comes across as a classic example of the idle brain growing increasingly suspicious and insecure of his wife's new found status. A feudal instance (albeit a little trite) shows him convincing her to resign and then urging her to continue when he himself becomes unemployed.
The friendship between Arati and an Anglo-Indian female colleague is another stroke of Ray's modernism. The friendship leads Arati on to suddenly give way to her impulsiveness and stand up for what she believed in. This follows with her resignation.
A strong and believing woman's trust in her husband is re-established and both walk out hand-in-hand into the alleys of a Mahanagar(a big city) which surely has some job in store for the TWO of them.