If the people in the poem "I hear America Singing" were speaking rather than singing, the tone will be less hopeful. The characters in the story were all singing as they go about with their works, showing that they are all Happy but if they were not singing and instead speaking, they will work everyday for the elite and be seen as people with no hope.
Furthermore, the poet wanted to present a Happy America, a joyous place hence the people in the poem were singing instead of speaking because when they sing,the tone becomes more hopeful but when they speak, it loses enthusiasm and becomes less hopeful.
Remember, major characters are those who are central to the main plot and story conflicts. ... Minor characters are there to support the major characters but have less influence on the story.
