There are ten stanzas of three lines each. The personified onion is the speaker, revealing its thoughts and feelings to the person who is cutting it. It is a metaphor where the onion is the unattainable truth in life that's pursued with such stubborn determination that everything is destroyed in the pursuit.
The onion tells the person that real truth is impossible to attain because she refuses to face the actual truth of life. The onion asks her, "Is this the way you go through life, your mind/A stopless knife, driven by your fantasy of truth,..." It also compares its layers to the layers of the person's facade that she presents to the world, the fake side that hides her real self. To know others,one must peel away the layers of a person to see who they really are.
The onion warns the person not to go after the truth so relentlessly and violently that her determination destroys everything in its path. Even the tears caused by the onion doesn't stop the person from cutting and peeling away the layers. "Look at you, chopping and weeping. Idiot." At the end, the onion makes a prophecy. "...Poor fool, you are divided at the heart,/Lost in its maze of chambers, blood, and love,/A heart that will one day beat you to death." Because the person has no center to give her peace and stability, her heart will continue to create desires that can never be fulfilled.