It's a poem because it rhythms and it it's is under Jump Rope Poem !
its an extended metaphor comparing life to stairs that it self is endless. you shouldn't give up even if your life was bad
I"m guessing United States, Western Expansion era? (Frontier Ma!)
Quite simply it is words of advice from a mother to her son about her struggles and his struggles.
I think that the extended metaphor is the actual title, "Mother to Son", and it is this because in the poem life is compared to a crystal staircase.
The Inspiration of Rita Dove's Poems
Rita Dove on What Makes a Classic Poem
Robert Pinsky on the Favorite Poem Project
The Cappadocian Poems of Aretaeus