Why did Phillis Wheatley believe that Christianity and slavery were incompatible

Since Phillis Wheatley was indoctrinated in the Christian faith at an age when she was able to reason complex subjects, she soon would learn that Jesus' teachings were mainly about love among individuals, and slavery was an institution that clearly attempted against that because of the exploitation of man by man and the harsh physical punishment that slaves had to undergo at the hands of plantation owners or foremen.