Edna St. Vincent Millay grew up in a very poor home. This fact did not deter her from becoming a famous author. Known for her poetry and plays, she was the first woman to receive a Pulitzer Prize for poetry.
Her poems typically speak to "love and loss, nature and change, life and death, art and beauty, justice, equality, and the predicament of women in American society." That said, "Feast" exists as an example of what her poetry focused upon.
"Feast" speaks to the challenges one faces in a socially unequal world, within a naturalistic atmosphere. The speaker's attempts to drink from a vine come up empty. One cannot actually drink from a vine (the fruit of the vine contains the craved liquid). The "gnawing" and eating of plants and roots leaves the speaker desiring more (given her thirst has yet to be quenched).
The last stanza speaks to the fact that she is in charge of feeding the grape and the bean for their owners. As a worker, she is not able to indulge in the fruits of her labor. Instead, her work makes her weary, and all she can do is lie next to the plants, starving and thirsting.
Therefore, the poem speaks to the inequalities of life. Those who own the plants do not have to work to bear their fruits; likewise, those who toil over the plants are not allowed to take of their efforts.