Why does douglass include the poem by john greenleaf whittier after he tells the story about his grandmother?

In this narrative, Douglas includes the poem Whittier by John Greenleaf because it refers to slavery.

He related the poem to his grandmother's own experience, due to the fact that she was a slave and died blind.

Besides that, all the text refers to slavery in general.

The author makes several points about slavery such us:

-No one can be enslaved if he or she has the opportunity to think, read and write

- Justice for slaves is very different from justice for whites, among others

d. murder of a son and cooking the son for a feast

procne murdered her son and served him to tereus, her husband and her son's father. she did this out of revenge. tereus raped her sister, philomela, and cut her tongue out to keep her from talking. philomela managed to communicate it to procne and procne sought revenge.

tantalus murdered his son and fed him to the gods because he was angry with the gods. the gods punished him by putting him in a pool of water that evaporates when he tries to drink and having fruit hang just out of his reach.