Most chapters of The Souls of Black Folk begin not with songs but with extracts of poetry written by famous white people, such as Whittier or Elizabeth Barrett Browning. One chapter even opens with a verse by Schiller, quoted in German.

Du Bois has two purposes in starting each chapter this way. First, each quote encapsulates the main theme or message of the chapter it heads. If you are at a loss for what Du Bois hopes is your "takeaway" from a chapter, you need only read and understand the words of the opening verse. For example, in chapter 3, Du Bois offers a critique of Booker T. Washington, stating that Washington "unmans" blacks by urging them to capitulate to whites and accept a second-class status. Instead, Du Bois says, blacks need to push back and fight for full equality. The quote he provides, from Byron's Childe Harold's Pilgrimage, supports this theme, criticizing the Greeks for being too subservient in the struggle for freedom and urging them to fight:

From birth till death enslaved; in word, in deed, unmanned!
******
Hereditary bondsmen! Know ye not
Who would be free themselves must strike the blow?

Second, although he is writing to both blacks and whites, Du Bois wants to catch the attention of whites, for as he states in the book, the black quest for equality cannot succeed without white support and encouragement. His quotes appeal to whites by showing that whites themselves have expressed the same sentiments about freedom, desire, and dignity that he does and by showing them he has the education and intelligence of a white person, even to the point of knowing German. These verses therefore help him build his ethos, or credibility.

WEB Du Bois begins each chapter with both a quote (from some famous literary verse) and lyrics from a Negro Spiritual or other African American music passed down by oral tradition.

Du Bois' primary idea behind the entire work is to show what life is like for black people in America in the 1900s.  He is convinced that race is the primary problem facing the upcoming century (and he turns out to be right).  The framing of each chapter with poetic quotes and negro spritual lyrics shows that Du Bois means to draw on the support of what is already established in "White" America, and to combine that with support from what is established in the hearts and souls of his people, or "Black" America.  It is an attempt to make peace from the outset - he is not proclaiming a radical revolution or war-like rise out of oppression into equality.  Rather, he wants to paint a picture (through the artform of writing) that shows the beautiful combination of two cultures - working together to eliminate conflict.