Nowhere in the New Testament will you find a condemnation of slavery, nor an updating of the Mosaic slave code. Instead you have stuff like Ephesians 6 where slaves are told to be “obedient to them that are your masters according to the flesh, with fear and trembling”; and Philemon, where Paul sends back a runaway slave to his Christian owner. Jesus does not raise a word against the practice.
How can this be? If slavery is a human evil, how can the Master and his servants have had nothing to say against it?
Therein lies the answer. For Jesus and Paul, the master-servant (= slave) relationship was both a fact of life (not dissimilar to employer-employee, father-son) and a sign of all our client relationships with God. Jesus uses this relationship in the parable of the faithful steward (Luke 12:43-48):
Blessed is that servant, whom his lord when he cometh shall find so doing [acting faithfully].
Of a truth I say unto you, that he will make him ruler over all that he hath.
But and if that servant say in his heart, My lord delayeth his coming; and shall begin to beat the menservants and maidens, and to eat and drink, and to be drunken;
The lord of that servant will come in a day when he looketh not for him, and at an hour when he is not aware, and will cut him in sunder, and will appoint him his portion with the unbelievers.
And that servant, which knew his lord’s will, and prepared not himself, neither did according to his will, shall be beaten with many stripes.
But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more.
Here the Christian becomes the vilicus, or houshold steward (still a slave; think of Joseph in Potiphar’s house); Christ is the absent paterfamilias who will return to reward or punish him according to his faithfulness.
For Jesus and Paul then, because we all live in a client relationship (God-Man; or better, Christ-Christian), extending that relationship to human interactions is not morally problematic. As such, slavery requires no condemnation for we are all slaves. All that remains is for slaves to “fear” their masters; and for masters (who are not the real masters, only the stewards), to not beat their slaves and otherwise act like delinquents.
Moral? Even Jesus’ words in the New Testament are wedded to their time.