The slavery question is complex, but I want to share a few thoughts regarding why Jesus didn’t outright abolish slavery and why slavery is not advocated against in the New Testament.
Throughout scripture, God typically works from the inside out. He’s a God that cares that the cup is clean first on the inside and then on the outside. Outside appearance (if one seems good) is much less important than the heart of a person (if ones thoughts and desires are good). When it comes to slavery, it is the same idea.
How can we transform a corrupt and wicked system? Can we do it by forcing people to follow set rules and patterns? This almost never works. I don’t think many people would advocate slavery as an ethical system irregardless of their views on slavery for productivity or economical reasons. Yet, various forms of slavery have and do exist. It seems such tendencies of selfishness and ownership go hand in hand with human nature. And if this is the case–if slavery is a manifestation of unethical thoughts and desires within certain people–then the solution is to change those thoughts and desires. Would it be possible to transform the hearts of the masters to such an extent that they willingly set their slaves free? If so, this would be more efficient than forcing abolition.
So, instead of coming to the masters (the rich, the intelligent, the beautiful, the healthy, the prosperous), Jesus comes to the slaves (the poor, the weary, the beaten, the imprisoned, the prostitutes, those in physical slavery). Instead of dictating a system of rules to the ones who lead the world, He comes to the ones who are owned and weak and weary within the system. And what would you say to those ones? Slavery is wrong, it should be abolished? This is obvious. No need to tell the slave that he shouldn’t be owned–he knows that already. Instead, Jesus gave to the slaves and the lowly–to everyone who would listen–a better gift: an inner freedom.
Jesus did free the slaves, but He freed them from feeling oppressed. He promises that in Him is fullness of joy, perfect love, unprecedented peace, and hope that one day the corrupt system will be overturned in a physical way when He comes again to rule as King of the earth. This is an inside out process. The slaves receive freedom beyond what their masters are capable of experiencing. Oh the irony that those who think they are free are not while those who are physically oppressed can be free! But then the slaves can pass this freedom on to the masters, and as the masters are renewed internally they can begin to change the system. In this way, the weak minister to the strong. It is one of the great biblical paradoxes.
The fullness of this process has not yet come. God is still working to grant freedom to new hearts. But a time is coming when everyone picks a side–for God or against Him–and when that time comes, the Lord Himself will return to earth to free us in a physical way from the corruption of the world systems.