Luke 4:18 has a mention of “freeing prisoners” but that is certainly not a call to end slavery.
It says “to set at liberty those who are oppressed.” By any use of the term, slaves can be said to not have liberty and to be oppressed.
And you are ignoring something very important. No, Paul and other New Testament writers are not calling for the abolition of slavery, but they are radically redrawing the identities of the Christian household. Masters relate to their slaves not as owners but as family, brothers in Christ.
Ephesians 6 doesn’t tell the slave owners to release their slaves. It does tell slaves to fear and respect their masters and do as they are told. This sure seems like a call to maintain the practice. The fact that Paul here equates serving a master with service God seems to be a healthy endorsement of it, despite an aside in 1 Timothy 1:10.
I never said Ephesians told Christians to release their slaves; what I said was “Christianity taught equality between masters and slaves.” This is what Ephesians 6:5-9 actually says:
5 Bondservants, obey your earthly masters with fear and trembling, with a sincere heart, as you would Christ, 6 not by the way of eye-service, as people-pleasers, but as bondservants of Christ, doing the will of God from the heart, 7 rendering service with a good will as to the Lord and not to man, 8 knowing that whatever good anyone does, this he will receive back from the Lord, whether he is a bondservant or is free. 9
Masters, do the same to them, and stop your threatening, knowing that he who is both their Master and yours is in heaven, and that there is no partiality with him.
Paul commands masters to serve their slaves just as he has told slaves to serve their masters, essentially, treat each other fairly and sincerely and be good to each other for the sake of their love for Christ. In the context of ancient slavery, this is radical; it is also in line with Jesus’s views on leadership, “whoever would be great among you must be your servant” (Matthew 20:26).
1 Timothy 1:10 cannot be merely dismissed as an “aside.” It unequivocally declares the slave trade to be sinful. When you think of this, it makes sense. Slave traders are after all taking and then selling what does not belong to them–the lives of other people.
1 Corinthians 7:21 is more a call to not concern oneself with being a slave and in fact says one "should remain in the situation they were in when God called them.
Come on now. Paul writes, “Were you a bondservant when called? Do not be concerned about it. (But if you can gain your freedom, avail yourself of the opportunity.).” Yes, Paul says do not worry over life situations you cannot change, but if you can change your situation he tells them to go ahead and do it. This is not an endorsement of slavery.
Context is everything here. Paul believed (as many modern Christians also believe) that the return of Christ was imminent. He does not want Christians to be anxious about their situations in life because, as he says, this entire world is going to end soon anyway and a new one take its place. This is all explained in 1 Corinthians 7:29-31:
29 This is what I mean, brothers: **the appointed time has grown very short. **From now on, let those who have wives live as though they had none, 30 and those who mourn as though they were not mourning, and those who rejoice as though they were not rejoicing, and those who buy as though they had no goods, 31 and those who deal with the world as though they had no dealings with it.
For the present form of this world is passing away.
That combined with Galatians 3:28 where it equates worship God with serving a master certainly gives a push to the worthiness of slavery. That passage in Galatians, while it does claim that all men are equal with respect in their need to worship Jesus, it ignores that God was the one who called for and spelled out how one man can do grave harm to another and call it good in his eyes.
The fact that God allows something does not mean he calls it good. He allowed polygamy as a concession to human weakness, but Christ taught us a better way. Galatians 3:28 teaches us that the master and the slave are one in Christ. They are brothers in Christ. The Christian master should therefore treat his slave as part of his family, as a brother.
Paul doesn’t call for the ending of slavery and God (any of the three persons) certainly does not call for it. It simply doesn’t add up to say that because God calls us to love one another that overtakes God telling a man how to sell his daughter into sex slavery or how perfectly fine it is to beat a slave because he’s his property.
Paul calls the slave trade sin. He teaches masters to love and serve their slaves, and he instructs both masters and slaves to see each other as brothers and sisters united in Christ.
And, as I said above, this theological perspective does eventually lead to the demise of slavery in the West, because as hard as Christians tried to justify slavery using Old Testament texts, the New Testament context of Christian masters and Christian slaves being brothers undermines the entire social structure on which a slave society is built.