Slavery is the condition of bondage or ownership of persons. The regulation of the slave trade is discussed at length in both the Bible and the Qur'an. This sanctioning of slavery shows that these is not a highly moral books but instead reflects cultural norms at the time they were written.
Slavery in the Old Testament
Slavery is explicitly regulated and clearly endorsed in the Old Testament in several instances. The New Testament recognizes that the institution of slavery exists, but it doesn't make any attempt to criticize it. Apologists attempt to redefine slavery in the Old Testament by equivocating between Hebrew and non-Hebrew slaves. The Bible treats them as distinct groups. This is an example of Christians' selective use of Old Testament law.
Slavery of non-Hebrews is implicitly condoned in the Old Testament in several instances.
- Exodus 21:20-21 and Exodus 21:26-27 regulates the beating of slaves, and states that the owner may not be punished if the slave survives for at least two days after the beating.
- Exodus 21:28-32 if a man negligently lets his bull gore someone to death, they are to be killed - unless a slave was the victim in which case the owner shall be compensated.
- Leviticus 19:20-22 gives instructions about the sacrifices that should be made if a slave owner has sex with or rapes an engaged female slave. The slave herself is punished with whipping, but no sacrifices or punishment are required if the slave is not engaged.
- In Leviticus 25:44-46 , the Israelites were allowed to buy slaves from other nations, keep them for an unlimited time and then hand them down as an inheritance since they are property.
- Deuteronomy 20:10–11 If a city surrenders during war, its inhabitants may be enslaved. "This meant slavery in the full force of that word." 
- Deuteronomy 21:10-13 You can force a marriage with a slave woman taken during war time.
- 2 Samuel 12:31
There so no prohibition for having sex with slaves, since they are considered to be property (which today would be considered rape), as long as the slave was not already engaged. In fact, this arrangement is approved by Numbers 31:17-18 Exodus 21:7-8 .
Indentured service was an option available to Hebrew people. For men, this was a time limited contract that exchanges labor for certain benefits, in which the laborer could not usually terminate the agreement. Women remained slaves permanently.
- Exodus 21:2-6 males that are indentured with a wife shall be released with his wife. Male servants that are given a wife (and may have children) are released but their family is not. They have the option of being a permanent servant (i.e. a slave in all but name).
- Leviticus 25:38-43 Hebrews may be bought but only for a limited time and may not be worked ruthlessly. This implies that non-Hebrews may be worked ruthlessly.
Slavery in the New Testament
The second part of the Bible recognizes that the institution of slavery exists, but it doesn't make any attempt to criticize it.
- In Luke 12:45-48 , the Parable of the Faithful Servant, Jesus discusses the punishment of slaves, and says that a slave may be punished for not doing something he wasn't instructed to do.
- In Ephesians 6:5-9 , Paul instructs the slaves to be obedient.
- 1 Corinthians 7:21-23
- Colossians 4:1 also admonishes slaves to obey their masters.
- In his Epistle to Philemon, Paul is allegedly returning a runaway slave to his owner.
- In Matthew 18:25 , people and their children are described as being sold into slavery.
- Colossians 3:11 , 1 Corinthians 12:13 and Galatians 3:28 are sometimes used to defend NT, to show that it supports some form of egalitarianism.
- 1 Timothy 1:10 this verse condemns "manstealers" or "kidnappers". This only refers to illegal slave trading, rather than the established slave trade. Some translations wrongly use the word "slave traders". 
- 1 Timothy 6:1-3 slaves should respect their master. Masters should respect their Christian slaves (which implies they may abuse their non-Christian slaves).
Some arguments attempt to redefine the word "slavery" into something that Biblical scripture doesn't match, for instance:
- Redefining slavery in the Bible to be less offensive, more like indentured servitude, and wasn't like slavery as defined in U.S. History.
- "It is important to note that neither slavery in New Testament times nor slavery under the Mosaic Covenant have anything to do with the sort of slavery where “black” people were bought and sold as property by “white” people in the well-known slave trade of the last few centuries."
- Redefining slavery to be so extreme that the Bible's mentions don't qualify. E.g. that slavery is when people are worked 24/7, without and food, water or sleep.
These are semantic games, trying to rationalize the Bible's position on slavery. The debate can be brought back into focus if the apologist is asked whether he/she thinks it is moral for one human being to own another, even for a short duration. Then, the Biblical scripture can be quoted to re-establish this concept, regardless of whether the word "slavery" is used or not.
Apologists attempt to redefine slavery in the Old Testament by equivocating between Hebrew and non-Hebrew slaves. The Bible treats them as distinct groups. The Bible allows for both indentured servitude (for Hebrews only, a time limited contract that exchanges labor for certain benefits, in which the laborer could not usually terminate the agreement) and slavery (for non-Hebrews, without time limit) as distinct things. Also, indentured servitude is arguably immoral since it can be used to exploit vulnerable people.
Some apologists claim that Old Testament slavery was not based on force. Forceful enslavement was allowed Deuteronomy 20:10-11 Deuteronomy 21:10-13 and occurred many times in the Old Testament, including Moses enslaving captive virgin women (and ordering the slaughter of the rest). Numbers 31:10-18 . See also 1 Kings 9:15 , 1 Kings 12:18 . The Bible explicitly says slaves are property that may be kept for an unlimited time. Leviticus 25:46 The "good treatment" of slaves specified in the Old Testament only prevents their owner from beating them to death, knocking out their teeth or blinding them. Exodus 21:20-21,26-27 There is no significant difference between Biblical non-Hebrew slavery and historic slavery in the United States.
Apologists often argue that those enslaved either deserved it, those enslaved were from a particular tribe that God ordered an assault upon, or it was for the slave's own good.
- "Because of the socioeconomic situation of Old Testament Israel, God did allow slavery, but He allowed it for a simple purpose: to help the poor survive. [...] Foreign slaves were not automatically released after six years; foreigners were not allowed to own land in Israel, and it would have been next to impossible for them to earn a living on their own; to release such slaves against their will may have been cruel."
- "Maybe [slavery] was a way of dealing with prisoners of war rather than killing them?"
Contemporary morality considers slavery as never justified. The apologist is essentially arguing that slavery is acceptable in some circumstances. If there were problems that slavery could address, those problems almost certainly have a better solution available - particularly for an omnipotent God.
Some apologists argue that it was "a different culture and a different time". This implicitly accepts moral relativism, which is contrary to Biblical morality.
Denying the Bible's stance on Slavery
Occasional Bible verses are used to argue that the Bible was actually against slavery, such as:
"And he that stealeth a man, and selleth him, or if he be found in his hand, he shall surely be put to death."
- — Exodus 21:16 (NIV)
This, however, is ignoring significant context. Surrounding this verse is also written many rules that say one can own slaves. Exodus 21 It's readily understandable that references to "a person" or "a man", is talking about an existing slave, and what the slave does, or what's done to the slave. In this reading, "stealing a man" is talking about stealing someone else's slave. The problem here is not slavery, but stealing.
"For whoremongers, for them that defile themselves with mankind, for menstealers [also translated as "slave traders"], for liars, for perjured persons, and if there be any other thing that is contrary to sound doctrine;"
- — 1 Timothy 1:10 (King James Version)
This verse condemns "manstealers" or "kidnappers". This only refers to illegal slave trading, rather than the established slave trade. Some translations wrongly use the word "slave traders". 
If verses like this are brought up, consider asking the apologist why this specific verse matters, but the others don't, despite the supposed anti-slavery verse being outnumbered by the pro-slavery verses.
Christians abolished slavery
- "Slavery is one of the best examples — far from being a Western Christian invention, it was ubiquitous, and it was only the Christian west that abolished it."
Slavery was often imposed on other cultures by Christian colonialists. The Atlantic slave trade was created and operated by Christians, so abolishing it was really the least they could do. Christian slave owners often used the Bible to defend slave ownership.
- "At best, one could say that these cultures belatedly realized the evil of slavery only after they themselves had instituted it and caused it to flourish for hundreds of years, and finally corrected their own mistake."
Historical defense of American slavery
Many Christians were abolitionists and openly opposed slavery. However, other Christian supporters of slavery also justified their arguments with reference to Bible verses like those listed above.
For example, in 1856 Reverend Thomas Stringfellow, a Baptist minister from Culpepper County in Virginia, wrote an essay called A Scriptural View of Slavery, which is full of passages that support his opinion, such as: 
- "Job himself was a great slave-holder, and, like Abraham, Isaac, and Jacob, won no small portion of his claims to character with God and men from the manner in which he discharged his duty to his slaves."
- "It is certain that God interposed to give Joseph the power in Egypt, which he used, to create a state, or condition, among the Egyptians, which substantially agrees with patriarchal and modern slavery."
- "If, therefore, doing to others as we would they should do to us, means precisely what loving our neighbor as ourself means, then Jesus has added no new moral principle above those in the law of Moses, to prohibit slavery, for in his law is found this principle, and slavery also."
While slavery pre-existed Islam, it continued in Islamic countries for many centuries. Muhammad himself bought, sold, captured, and owned slaves. Sharia law specifies limited conditions, mainly prisoners of war, in which a person may be enslaved. This practices is also supported by the example of Muhammad, whom Muslims normally try to emulate.
"[Allah] makes them their property by means of slavery unless the ruler chooses to free them for nothing or for a ransom, if that serves the interests of the Muslims."
- — Adwa’ al-Bayaan 3/387
"O Prophet! We have made lawful [for sex] those (slaves) whom thy right hand possesses out of the prisoners of war whom Allah has assigned to thee"
"And it is not permissible for a man who believes in Allaah and the Last Day to have intercourse with a captured woman until he has established that she is not pregnant."
- — Abu Dawood, 2158; classed as hasan by Shaykh al-Albaani in Saheeh Abi Dawood, 1890.
Apologists argue that the Qur'an only allows slaves to be ransomed or released but not enslaved (TMQ 47:4).  This principle is arguably violated by Muhammad's own actions. The Qur'an states that it is lawful for a man to have sex with female slaves that he owns Surah 4:24 ; consent is not required and by modern standards, he can rape them.
However, the Qur'an does make a virtue out of freeing slaves and treating them well in most respects. The Qur'an does not directly call for the abolition of slavery.
- "Although Islam is much credited for moderating the age-old institution of slavery, which was also accepted and endorsed by the other monotheistic religions, Christianity and Judaism, and was a well-established custom of the pre-Islamic world, it has never preached the abolition of slavery as a doctrine. "
- "Islamic law and custom provided no basis for the abolition of slavery or even for the curtailment of the slave trade. "
The vast majority of Muslims condemn slavery and it is universally banned by secular law. However, it seems contradictory that such measures are needed to improve on the supposedly "perfect" Sharia law. On the other hand, it is possible that the circumstances of enslaving someone can no longer be met, while slavery would technically be legal, it would make slavery illegal in practice. A minority view in contemporary Islam is that slavery is still a valid practice:
- "Slavery is a part of Islam. Slavery is part of jihad, and jihad will remain as long there is Islam. "
Islam abolished slavery
"I mean, if you know anything about Islamic history the very first thing that Muhammad did was outlaw slavery"
Unfortunately, that is not the case. Islam explicitly allows for slavery.
- They kept us as slaves: AP reveals claims against church, AP, 25 July 2017
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- ↑ Forough Jahanbaksh, Islam, Democracy and Religious Modernism in Iran, 1953-2000, 2001
- ↑ Bernard Lewis, The Shaping of the Modern Middle East, 1994
- ↑ Shaikh Salih al-Fawzan "affirmation of slavery" was found on page 24 of "Taming a Neo-Qutubite Fanatic Part 1" when accessed on February 17, 2007
- ↑ 
- Slavery in Islam, BBC
- Converted2Islam, Discussion of Quran 4:24, 20 Jun 2016
- What the Bible says about slavery at Religious Tolerance
- Christianity and History: Bible, Race & Slavery at Atheism.about.com
- Scriptural and Statistical Views in Favor of Slavery (full text)
- Christian apologist defending slavery, The Atheist Experience, 3rd Nov 2013