One of Walter Johnson's central arguments in Soul by Soul is that slaveholders often represented themselves to each other by their slaves. What this means is that those who owned slaves were effectively slaveholders first and individuals second.
Or, to put it another way, one could say that slaveholders were primarily defined not by who they were but by what they did as economic participants in the slave market. It was from such involvement in the buying and selling of human chattel that they derived their social status, which remained exalted in antebellum Southern society.
In support of his argument, Johnson cites the fact that discussion of the slave market was extensive in slaveholders' letters, much more so than the subject of dueling upon which many historians have become somewhat fixated. This indicates the extent to which the ownership of slaves and everything associated with it formed the center of a slaveholder's universe.
In sitting down to write letters, the primary substance of social relations in the antebellum South, slaveholders self-consciously sought to produce social representations of themselves, self-constructed identities that they then offered to their correspondents, especially other slaveholders.
Being a slaveholder wasn't just an economic activity, a job that could be put aside and forgotten about at the end of a working day. It was a whole way of life from which those who engaged in it were able to carve out a distinct social identity.
In turn, this conferred a wholly undeserved degree of social respectability upon slaveholders that made them valued members of Southern society. So long as this was the case, slaveholders would continue to represent themselves to each other through the slaves that they owned, safe in the knowledge that society as a whole didn't think that they were doing anything wrong.