It was used manipulate the slaves and to justify slavery as a christian act.

When a man strikes his male or female slave with a rod so hard that the slave dies under his hand, he shall be punished. If, however, the slave survives for a day or two, he is not to be punished, since the slave is his own property. (Exodus 21:20-21

Slaves, obey your earthly masters with deep respect and fear. Serve them sincerely as you would serve Christ. (Ephesians 6:5 NLT)

However, you may purchase male or female slaves from among the foreigners who live among you. You may also purchase the children of such resident foreigners, including those who have been born in your land. You may treat them as your property, passing them on to your children as a permanent inheritance. You may treat your slaves like this, but the people of Israel, your relatives, must never be treated this way. (Leviticus 25:44-46 NLT)

The Bible in general is often pretty pro-slavery, New Testament included.

For example, the NT book of Philemon can easily be read as a defense of slavery. Paul tells a runaway slave that he should return to his master. While a modern reading of Philemon often focuses on forgiveness, reconciliation and slavery as a context for freedom through/bondage to Christ, it's very easy to read Philemon as a pro-slavery text.

In fact, the Pauline doctrine of imminent eschaton is sort of pro-slavery in general. Paul encourages everyone who believes in Jesus to maintain their status quo until the Christ returns.

17 However that may be, let each of you lead the life that the Lord has assigned, to which God called you. This is my rule in all the churches. 18 Was anyone at the time of his call already circumcised? Let him not seek to remove the marks of circumcision. Was anyone at the time of his call uncircumcised? Let him not seek circumcision. 19 Circumcision is nothing, and uncircumcision is nothing; but obeying the commandments of God is everything. 20 Let each of you remain in the condition in which you were called.

21 Were you a slave when called? Do not be concerned about it. Even if you can gain your freedom, make use of your present condition now more than ever. 22 For whoever was called in the Lord as a slave is a freed person belonging to the Lord, just as whoever was free when called is a slave of Christ. 23 You were bought with a price; do not become slaves of human masters. 24 In whatever condition you were called, brothers and sisters, there remain with God.

1 Corinthians 7