This is a follow up to my question here. There, I asked about an inscription inside the Jefferon memorial that says:
God who gave us life gave us Liberty. Can the liberties of a nation be secure when we have removed a conviction that these liberties are the gift of God? Indeed I tremble for my country when I reflect that God is just, that his justice cannot sleep forever. Commerce between master and slave is despotism. Nothing is more certainly written in the book of fate than that these people are to be free establish the law for educating the common people. This is the business of the state to effect and on a general plan.
I am puzzled about
Commerce between master and slave is despotism.
Where was there commerce between master and slave back then, and if there were such commerce, was it despotism? Why would that be of great concern to Jefferson, and why would the designers of the memorial have selected that as part of a inscription inside the memorial?