I don’t think the poem can convey the right idea without this metaphor in the poem. The narrator is the poem is a Black American woman. Life for the Blacks was very hard in the America of the past. Things have changed for the better and we even see the first Black President in Barak Obama. But when Langston Hughes was writing this poem, it was impossible to even imagine that a Black man would become the President one day. The Blacks had to struggle even for their existence.
It was with great difficulty they found even decent livelihood. So the mother is telling her son that she had been working hand to reach even where she has reached. Life is a journey, an upward journey and we use stairs. But here the stairs are full of tacks and splinters. There are dark comers and there are no carpets. Every turn there are problems and obstacles. So it needs courage to go on. Such an idea could be conveyed only through the metaphor of the non crystal stairs.
