Biblical slavery is cited by atheists as an objection to the Bible and Christianity.

In modern Western thinking, the essential nature of slavery is epitomised by the history of Black African American slavery. A study of the Bible shows that the essential nature of Black African American slavery, which made it so oppressive and wrong, was prohibited by God in the Old Testament law.

Challenging Scriptures

Genesis 16:1-16; 21:9-21 Hagar, who bore Abraham a son, and was treated harshly by Sarai. Later Sarah was jealous of them, and Hagar and Ishmael were sent away.
Exodus 21:4 If master provides a wife, when the servant leaves then the wife stays with the master.
Exodus 21:7-11 Selling a daughter as a maidservant or wife.
Exodus 21:20-21 On beating a slave nearly to death.
Leviticus 19:20-22 Rules re someone who sleeps with a concubine, a slave woman.
Leviticus 25:44-46 Making slaves of surrounding nations, for life, not for a 6-year limit as for Israelites.
Deuteronomy 20:14 In war, women and children can be taken as "plunder".
Joshua 9:3-21; 1 Samuel 21:1-14 The case of the Gibeonites.

Exodus 21:20-21

It doesn't say it's okay to beat your servant. Reading in its context, it is talking about the circumstances in which to administer the death penalty (if you kill someone), followed by laws about compensation in the case of injury.

In verses 12-15, it says the death penalty is due for someone who murders another person. But if someone didn't kill a person, the death penalty is not appropriate. In verses 17-19, it talks about appropriate payment of compensation for their loss of work time, and provision for them to heal, if someone injures another person.

Then, in verses 20-21, it specifies how the law applies for a servant. Namely:

• The death penalty is also applicable for servants. Ie they are not second-class citizens; the law about the death penalty is the same regardless of the status of the victim.
• In the case of injuring a servant, the compensation for their loss of work time is already born by the master, because the servant normally works for their master, so the master inherently bears the loss.

Old Testament

Hebrew ebed may be translated slave, servant.

Exodus 21:2-11 Rules for Israelites. Serve 6 years then release. Exception requires ear pierced with awl.
Exodus 22:3 A thief had to repay what they stole, or else be sold if they had nothing with which to repay.
Leviticus 25:39-43 Rules for Israelites: hired servants, not slaves. Release in Jubilee.
Leviticus 25:44-46 Rules for foreign slaves.
Leviticus 25:47-55 Rules for foreigners buying Israelites as slaves, and rules of redemption, Jubilee.
Leviticus 26:13 God freed the Israelites from slavery in Egypt. He broke their yoke. Symbolic of spiritual freedom from sin we suspect.
Deuteronomy 15:12-18 Rules for Israelites as servants. Serve 6 years then release, not empty-handed but with generous gifts. Exception requires ear pierced with awl.
Deuteronomy 29:11 It sounds as though the foreigners who came out of Egypt with Israel worked as labourers/servants in some capacity: "stranger... who cuts your wood... who draws your water".
Joshua 9:22-27 Gibeonites tricked Israel, and became slaves instead of being killed.
1 Kings 5:13-17 Solomon raised a labour force out of Israel.
1 Kings 9:20-22; 2 Chronicles 8:7-10 Solomon used foreigners, the remaining people of Canaan, for forced labour.
2 Chronicles 2:17-18 Solomon conscripted the aliens in Israel to help build the temple.

Reason for Slavery

It seemed it was something people did, or had compelled on them, due to:

• Financial trouble, poverty. Leviticus 25:35-43
• Unpaid debts. 2 Kings 4:1
• Repay liability (damages).
• Repay theft. Exodus 22:1-4
• Choice. Genesis 15:2-3; Exodus 21:5-6; 1 Chronicles 2:34-35

Nehemiah 5:1-13 Israelites charging usury, enslaving their brethren.

New Testament

Greek doulos may be translated slave, servant, bondservant.

Acts 17:26 And He has made from one blood every nation of men to dwell on all the face of the earth... No race or ethnic group should be treated as lesser people or less than human.
1 Corinthians 12:13 Whether Jew or Greek, slave or free, we are baptised into one spiritual body by one Holy Spirit.
Galatians 3:28 There is neither Jew nor Greek; slave nor free; male nor female; you are all one in Christ Jesus.

The book of Philemon has an intriguing letter from Paul to Philemon, about a servant Onesimus. Reading between the lines, it appears that Onesimus ran away from Philemon, and somehow ended up with Paul, and came to conversion while with Paul.

Addressing slaves

1 Corinthians 7:21-23 Advice to called people, who are slaves/servants.
Ephesians 6:5-8
Colossians 3:22-25
1 Timothy 6:1-2 Serve masters well, whether unbelieving or believing.
Titus 2:9-10

Addressing masters

Ephesians 6:9 "Do the same to them" ie be their servants, as in the golden rule.
Colossians 4:1

Protections

Exodus 20:8-11; Deuteronomy 5:14-15 Servants also to have Sabbath day rest (Deuteronomy 5:15 says it more explicitly).
Exodus 21:2-6 Israelites were only to be servants for up to 6 years.
Exodus 21:16 No kidnapping. Also Deuteronomy 24:7.
Exodus 21:26-27 Let a servant go free if they are injured, eg eye or tooth.
Exodus 22:21; 23:9 No oppression of foreigners among you.
Leviticus 19:13 Don't cheat a hired worker. Don't even delay in paying him by so much as one day.
Leviticus 19:33-34 Love the foreigners who dwell among you, as a native person, as yourself. Remember being strangers in the land of Egypt.
Leviticus 25:43,53-55 Don't rule over servants "with rigour". (Unclear in v53-55 whether it's talking about foreigners or not.)
Leviticus 25:39,47 Reason for becoming a servant: sell oneself due to poverty. Being a servant is an institution to protect the poor.
Leviticus 25:47-52 Rules of redemption. There was a process for obtaining freedom at a reasonable price (yet, freedom had a cost).
Deuteronomy 10:17-19 God is without partiality, caring for the vulnerable people. So love the stranger, like God does.
Deuteronomy 12:10-12,18-19; 16:11-15 In festival celebrations, include servants, Levites. Remember you were slaves in Egypt.
Deuteronomy 15:11-16 Be generous to the poor among you.
Deuteronomy 23:15-16 Don't return an escaped slave. Let him live in the land where he chooses.
Deuteronomy 24:7 No kidnapping an Israelite. Also Exodus 21:16 which doesn't specify an Israelite.
Deuteronomy 24:14-15 Don't oppress hired servants, whether Israelite or foreigner. Give them their due wages every day, because they are poor and need it.
Deuteronomy 24:17-19 Justice for widows, orphans, foreigners.
Deuteronomy 24:20-22 Leave portions of your crops for widows, orphans, foreigners.
Nehemiah 5:1-13 Nehemiah calls for the end of oppression of fellow Israelites through usury, and taking their land, which was sending them into slavery.
Job 31:13-15 Job acknowledges his duty to treat servants justly, and God's just judgement on mistreatment of servants, since they too are children of God.
Isaiah 58:3-6 A call to end exploitation and oppression of hired workers.
Jeremiah 7:6; 22:3 Don't oppress a stranger, fatherless, widow.
Jeremiah 34:8-17 Judgement on Judah for ignoring the commands about Israelite slaves serving for only 6 years.
Ezekiel 18:7-8,12-13,16-18 God's warnings against sin, including oppression, withholding a pledge, usury, taking increase, neglecting the hungry and needy.
Ezekiel 22:7,29 God judged the Israelites for, among other things, oppression of the poor and the foreigners among them.
Amos 2:6-8; 8:4-7 Condemnation of exploitation of the poor, selling and buying them as slaves.
Malachi 3:5 Condemnation of exploitation of workers.
Matthew 7:12; Luke 6:31 Golden rule.
1 Timothy 1:10 Kidnapping is wrong.
James 2:8-9 Love your neighbour as yourself; don't show partiality.
James 5:4 Condemnation of partiality.

Spiritual Symbolism

Romans 6:15-23 Be slaves of God and His righteousness, not slaves of sin.
Galatians 4:21-31 Slavery used as a symbol of the Old Covenant, in contrast with the freedom of the New Covenant. Ishmael, son of Hagar bondage, compared to Isaac, son of promise.