Most liberals and progressives (and moderates probably too) are puzzled by the "blood hymns" popular in more evangelical circles.  Today, reading James Cone's The Cross and the Lynching Tree, he discusses their power in the black church.  I can't imagine this explanation, though, is available for those in the white power structure.

Instead of attempting to explain the saving power of the cross rationally, black Christians recognized it as a mystery, beyond human understanding or control.  In remembrance of Jesus' last week, leading to his death, blacks at Ebenezer and other black churches, celebrating the sacrament of "Holy Communion," raised their voices to acknowledge "a fountain filled with blood," "drawn from Immanuel's veins"; "blood," they believed, "will never lose its power," because "there is power in the blood," and "nothing but the blood."

When blacks sang about the "blood," they were wrestling not only with the blood of the crucified carpenter from Nazareth but also with the blood of raped and castrated black bodies in America -- innocent, often nameless, burning and hanging bodies, images of hurt so deep that only God's "amazing grace" could offer consolation.