David Walker compares the American Christian form of slavery to the ancient heathen Spartan manner slavery, and finds the Christian’s version of slavery far more removed from mercy the pagan Spartan version. He comments,  Using the past, Walker makes an appeal to his readers, who would more than likely consider themselves more enlightened and civilized than the extremely violent ancient Spartans. In this he appeals to, not so much, their logic, but to their pride. He attempts to shame them by showing that they are more barbaric in their treatment of their fellow man than barbarians were. However, he does not leave this appeal to their pride, and humanity as his singular argument against them, he attacks them from a more spiritual angle.
He hopes that this appeal to Christianity will for his people’s oppressors force them to take a deep look at themselves and ask themselves why, in contradiction to the teaching of brotherly love and mercy in their religion do they treat their fellow man, their fellow Christian, in such brutal ways.  
Olaudah Equiano in his Interesting Narrative, pleads with his audience to question their own adherence to their Christian faith. He asks them if they are really Christians, and if so, is their treatment of their African slaves in keeping with their religion. He asks,  The author chooses to call them nominal Christians. This assault on their commitment to their faith is a clever play on their guilt. He acknowledges that they are Christians, but he does not give them the full title of Christian, telling them that even he, a man born in pagan lands, can tell that their Christianity is lacking, though not totally absent. This way of argument also tells them what they have to do to become true Christians. It’s as simple as following the Biblical commandment that the quotes.
