Slavery was for the Church not a difficulty of doctrine, but a strain on the imagination. Aristotle and the pagan sages who had defined the servile or “useful” arts, had regarded the slave as a tool, an axe to cut wood or whatever wanted cutting. The Church did not denounce the cutting; but she felt as if she was cutting glass with a diamond. She was haunted by the memory that the diamond is so much more precious than the glass. So Christianity could not settle down into the pagan simplicity that the man was made for the work, when the work was so much less immortally momentous than the man. At about this stage of a history of England there is generally told the anecdote of a pun of Gregory the Great; and this is perhaps the true point of it. By the Roman theory the barbarian bondmen were meant to be useful. The saint’s mysticism was moved at finding them ornamental; and “Non Angli sed Angeli” meant more nearly “Not slaves, but souls.”
— A Short History of England (1917).