Theory:

Then good Saint Peter grew angry,
For he was hungry and faint;
And surely such a woman
Was enough to provoke a saint.

And he said, “You are far too selfish
To dwell in a human form,
To have both food and shelter,
And fire to keep you warm.
Explanation:
 
The actions of the woman had turned the good Saint Peter angry. Of course, she didn't know that it was Saint Peter who had come begging for food. But the woman knew he was weak and poor, and he was almost faint due to hunger. All he had asked was for a single cake. Yet, the woman was far too selfish to feed a hungry mouth.

Out of anger and hunger, the good Saint Peter cursed the woman. He said that she was far too selfish to lead a comfortable human life. She had plenty of food, a comfortable home, and even fire to keep her warm during the winters. But she lacked a human heart.

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The woman's actions provoked the saint

The line "you are far too selfish to dwell in a human form" raises a major philosophical question: What is to be a human? The woman had the form, but was she indeed a human? And where is humanity in the actions of the woman?

The phrase "to dwell in a human form" raises not only the question of humanity but also suggests the spiritual and theological idea that the body is only a material entity where the soul and spirit reside. Compared to the other living beings on earth, human beings enjoy a great deal of comfort. Yet, most of us take our privileges for granted and are more often blind to the sufferings of others, like the woman in the poem. Hence, Saint Peter claims that she was too selfish to deserve the life of a human being.
 
Meanings of difficult words:
 
S.No
Words
Meanings
1
ProvokeTo cause a reaction, especially a negative one; to make a person or an animal angry
2
DwellTo live in or at a specified place
Reference:
National Council of Educational Research and Training (2006). Beehive. A Legend of the Northland - Phoebe Cary (pp. 65 - 67). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.