The song is coming from the singers soul. He is expressing his feelings about how he and all blacks are being treated. The singer also takes pride in the music. His people created the blues and he is proud of that. It is a source for them to express themselves and be proud.
Jazz is their music and they can relate to what is being said.
His voice comes from his heart and how he feels about the situation. These two relate because they both talk about the dark beating rhythm of blues and how it speaks to the situation of blacks at the time. They also talk about getting rid of the weary and troubles of their situation and taking pride in what they are and that way having peace with themselves and being able to sleep at night. The two are related because they both speak about the troubles that the african americans had while they were in slavery. But at the same time they are trying their best to forget them and move on with their lives.