He wanted it to be a slave free state reserved for men to start over from England.
Oglethorpe wanted to create Georgia as a colony for men who had run into trouble in England but were not serious offenders. Providing them an opportunity to own land and start over. This is why Oglethorpe did not want slavery in the colony. This would prevent slaves providing labor and would keep landownership smaller than the plantations of Virginia and the Carolinas.
Oglethorpe was not successful in the long run. After he left the leadership position of the colony, the land was open to wealthier farmers. In addition, slaves were brought into the colony as a source of labor for the newly emerging cash crop plantations.