Answer: He made two arguments.
Explanation: 1. He argued that Abraham who was the chosen servant of God had slaves and that the conditions of slavery then was almost certainly worse than those of their own slaves, therefore if Abraham as exalted and morally upstanding in the bible as he was had slaves, then it was not morally wrong to possess slaves.
2. He made reference to both the old and new Testaments where there were evidence of slave possession; not in condemnation but texts which actually supportef and encouraged slave ownership.