Sometimes students confuse the author of a poem with the speaker of the poem. In fiction, readers readily assume that the person who tells the story is not the author himself; the author has generated a fictitious character and tells a story through that character's eyes. The same happens in poetry. While the author does sometime speak as himself or herself, he may also create a completely fictitious persona who presents the poem to readers. I always tell my students that they should not assume that the speaker, or poetic voice, is the author unless they have solid evidence to believe otherwise.
In this particular poem, Langston Hughes, an African American poet who wrote in the years leading up to the Civil Rights Movement, uses the poetic voice of a mother (noted right in the title) to convey an important message for a young man. This works well because of the relationships mothers often forge with their children, instructing them with firm and loving advice often based in their own life experience. In the end, this mother tells her son,
Don’t you fall now—
For I’se still goin’, honey,
I’se still climbin’,
And life for me ain’t been no crystal stair.
The motherly wisdom is just the poetic voice that this son needs. His mother has struggled through hardship and is still pressing forward, climbing the metaphorical stairs of life.
Poets use varying poetic voices to deliver a particular tone or theme, and the choice depends on the ultimate message they intend to create.