The Quran mentions the word slavery in at least twenty-nine of its verse. Most of these are Medinan and refer to the status of slaves. They talk about manumission and sexual relations. The references to slavery mainly contain broad and general propositions of an ethical nature rather than specific legal formulations.
The Quran uses the past tense when describing slavery, referring only to those living in bondage at the time of revelation. It meant that slavery was never compatible with the commandments of the Quran. The Quran did not promote slavery or praised it or condoned it.
The Qur'an recognized the existence of the practice of inequality between a master and a slave. It acknowledged the norms about the rights of the former over the latter. But the divine guidance stated that from a spiritual perspective, "the slave has the same value as the free man and the same humanity as the master." It was not an endorsement of the institution; rather, it was a reminder that slavery is against human dignity.
The Quran urged kindness to the slave and recommended their liberation by purchase or manumission. The freeing of slaves is recommended both for the expiation of sins and pure benevolence. It exhorted masters to allow slaves to earn or purchase their freedom. The idea was to lead the community to a slave-free world.
The Qur'an, however, did not consider slaves to be mere chattels; It acknowledged their humanity in references to their beliefs, their desire for manumission, and their feelings about being forced into prostitution and forced labor. In one case, the Qur'an referred to master and slave with the same word, rajul. Later, interpreters presumed slaves to be spiritual equals of free Muslims. For example, verse 4:25 urged believers to marry 'believing maids that one owned' and then stated: "The one of you is as the other," which the Jalaalayn interpreted as "You and they are equal in faith, so do not refrain from marrying them." The divine guidance recognized the human aspect of slaves by referencing them as members of the private household, sometimes along with wives or children.
The purpose was not to promote or sustain slavery but to eliminate it. It took Muslims some 1400 years to realize this intent, and now slavery is completely abolished legally in all countries, including the Muslim majority countries.
On having multiple wives, there is only one verse in the Quran, referring to polygamy.
"And if you have reason to fear that you might not act equitably towards orphans, then marry from among [other] women such as are lawful to you - [even] two, or three, or four. But if you have reason to fear that you might not be able to treat them with equal fairness, then [only] one - or [from among] those you rightfully possess. It will make it more likely that you will not deviate from the right course." (Surah an Nisaa - Women, 4:3).
This reference to polygamy, or having multiple wives, was discussed as a response to a specific social situation of war-torn society in seventh-century tribal Arabia. The purpose was not on multiplying wives but social justice in the context of the social structures prevalent.
Polygamy was a component of justice in widows' treatment, and it was mainly to offer appropriate care to orphans. Its purpose was to allow widows and orphans to be taken care of in a social structure where women usually did not have independent means of financial support, and orphans did not have any legal status to exist as responsible beings.
But the text was clear that polygamy was only permissible with full equality and justice. But the Quran warned that it would not be possible for a husband to treat all of his wives fairly. It virtually eliminated the possibility of polygamy in practical terms.
If we look at the verse in detail, we find that it talks of dealing with justly with orphans and talks to their male guardians who might assume their guardianship. The guardian was to carry his duties honestly. The marriage was also an option to ensure this. The assumption was that marriage to the orphan would give him a more significant stake in managing the financial responsibility. It did not say that all male guardians must marry their female wards.
The verse also emphasized justice towards wives. The Quran said: "And it will not be within your power to treat your wives with equal fairness, however much you may desire it; and so, do not allow yourselves to incline towards one to the exclusion of the other, leaving her in a state, as it were, of having and not having a husband. But if you put things to rights and are conscious of Him-behold, God is indeed much-forgiving, a dispenser of grace" (Surah an Nisaa- Women, 4:129)
Thus monogamy is the rule for marriages, and polygamy is not relevant in our world today because there are alternative venues available to secure justice.
The irony is in our inability to look at the Quranic verses in a consistent and relevant manner. While practicing slavery for almost 1400 years legally, we have declared it illegal and un-Islamic today. However, on polygamy, despite the Quranic emphasis on equality and justice and having one wife, we still support and find justification for it. It is this practice that the Quran challenged. It clearly states that divine guidance does not serve the interests of a specific group, gender, or race.