There is no simple, pure 'truth' about the origins or meaning of the blues. It is impossible to precisely define the blues, just as it is impossible to precisely define folk, because there are too many blurred boundaries between genres, styles and understandings of the music. The 'roots' of the music are important, but cannot be traced back along a single pathway to a single 'authentic' or 'pure' point of origin. Although I believe a knowledge of the history of the music, and the material conditions under which it was developed, are useful in aiding our understanding of the music.
We should also be careful not to reduce the form to some single characteristic. A number of people seem to believe that the 'essence' of the music is in its emotional qualities (which are clearly important). Here, however, we should be particularly careful; it is all too common to describe (originally) 'black' cultural forms in terms of emotion, spontaneity, rhythm, purity, etc. in (an implied) opposition to 'white' musical forms which are, therfore, rational, composed, melodic, etc. There are obvious racist implications to this. Although I hasten to add that I'm not suggesting that any of the above contributors is being in any way racist. Hang on whilst I try and get the lid back on this can of worms . . .