A theme is almost like an atmospherically setting and how something is presented
In "324", the speaker of the poem spends her Sundays at home. She draws a comparison to others, as she states that they mostly spend their Sundays in church. It can also be assumed that the speaker may be outside at her home, as she uses many images of birds, and mentions an orchard.
The theme of the poem is basically the American Discrimination. Discrimination is basically is a term which is used to define the difference b/w two groups on the base of some qualities etc. For example the American Discrimination was between black and white people.
