Walther states that he doesn't know of a better definition of the word "slavery" than that of Melanchthon, the magister germaniae. Melanchthon in 1556 said that 'Civil slavery, which is approved by God (as Joseph and Onesiumus were slaves), is the lawful removal of the ability of ownership, the freedom to choose one's vocation or employment, and to move from one place to another.'
Walther explores a number of scriptural passages to further reinforce his view of slavery. His conclusion is clear: "From all this we can conclude that according to Holy Scripture - The Old Testament, God did not initially institute slavery or servitude as he did the state of matrimony or civil authority. Neither did He institute absolute monarchy, the class of the poor or any other social burden in life. Rather He deemed them punishment for sin itself and considered them as a 'duty-relationship' based on the fourth commandment. Further, he declared slaves to be the indisputable property of their master in the tenth commandment, in societies where such a relationship is lawful, just as He confirmed all other worldly and civil freedoms, burdens, rights, duties, ownership, etc."
But Walther won't allow himself to be boxed in. He says: "We willingly agree, however, that if the Old Testament alone spoke of such slavery, there would still be room for the idea that the morality of such a relationship has not been proven beyond all doubts. The people of Israel received from God, through Moses, their civil laws. These civil laws, though, could not punish all that which is punished by 'moral law,' the law of the eternal will of God Himself. Therefore, because of the wickedness of man a lot could not beheld to be moral, but things were allowed which were directly in opposition to the 'moral law' in order to maintain civil peace, based on the old axiom: Aliud jus poli, aliud jus so i, a different law for heaven, a different law for the earth.' One might think that this relationship between master and slave could fall into this latter category."