Why has the phrase “I rise” been repeated in the last stanza in "Still I Rise" by Maya Angelou?

The poem "Still I Rise" by Maya Angelou is one of strength and perseverance in spite of suffering and tribulation. The words of this poem outline the option to remain on the ground when you are pushed down or to rise up against oppression and continue moving forward.
The entire poem is intended as a hymn of persistence and stubbornness, an unwillingness to remain defeated. The last stanza is especially evocative of this motif—repeating the phrase "I rise" over and over again to give the imagery that, even if the world pushes me down 1,000 times over, still I rise.
Maya Angelou was extremely famous for her perseverance and success as a social justice figure, and this poem is a kind of autobiography of her struggles, where she has to continually renew her strength and stand up in the face of oppression.