Jefferson, though he owned slaves, was a proponent of ending slavery within the United States. At least twice that I am aware of, once before the Declaration was penned, he attempted to have slavery abolished in the law. I will say that his personal belief was that blacks were indeed inferior to whites, and that along with emancipation should come a relocation of the blacks outside of the territory of the United States, but at heart, Jefferson believed the institution should be ended.
One of the quotes from Jefferson regarding slavery is the following, from a letter he wrote to John Holmes in 1820:
I can say with conscious truth that there is not a man on earth who would sacrifice more than I would, to relieve us from this heavy reproach [slavery], in any practicable way. the cession of that kind of property, for so it is misnamed, is a bagatelle [possession] which would not cost me in a second thought, if, in that way, a general emancipation and expatriation could be effected: and, gradually, and with due sacrifices, I think it might be. but, as it is, we have the wolf by the ear, and we can neither hold him, nor safely let him go. justice is in one scale, and self-preservation in the other
Jefferson was, by all accounts, a man who enjoyed material possessions. Most of his slaves were encumbered with debt from his borrowing against their value and it was not possible to free or sell those slaves without paying off the debt, which he was never able to do in his lifetime. Most of them were sold upon his death to pay off the debts he owed. Remember too that at this point in history, slavery, not just of blacks, but of anyone, was a common practice. Indentured servitude was also a common practice whereby a man sold his children into servitude for a period of time to serve as an apprentice and learn a trade or perhaps as a punishment for the commission of a crime as a means of exacting reparations for the damages incurred by order of a court.
I suppose, when viewed through the lens of our modern beliefs, the discrepancy can't be fully resolved adequately. That is why it is usually unreasonable to hold historic actions accountable to modern standards. The first civil rights act, legislated in 1875, was ruled unconstitutional because the Supreme Court found that the federal government lacked the authority to compel anyone to associate with those that they didn't wish to associate with. An inn, tavern, business, even a hack, was considered private property and to compel the owner of that property to associate involuntarily with anyone was ruled to be outside of the powers held by the federal government. Yet another indication that at the time of our founding the federal government was not empowered to act outside of the specific enumerated powers listed in the Constitution. Grover Cleveland, a Democrat and the only president to serve two nonconsecutive terms, vetoed a bill seeking to grant farmers in drought stricken Texas federal tax dollars to purchase seeds saying he found no such power granted to Congress or the federal government in the Constitution. It really has only been since the presidency of Woodrow Wilson that the modern thought of a powerful central government has taken root. Prior to then, there were actually Supreme Court rulings that stated the federal government alone was prohibited from the actions expressed in the Bill of Rights. It was understood that a state could indeed prohibit ownership of firearms, or establish a specific religion within that state as the state religion. It is only since the Supreme Court started selectively incorporating the Bill of Rights as a complete prohibition that we have have come to believe that the states had no authority to do that which the Bill of Rights prohibited the federal government from doing.
