Looking up the meaning of slave and slavery and their alternative words in the Arabic language (abd and aubodeiah) in both Arabic and English dictionaries, we can understand that these words are not limited to the ancient practice of selling and owning humans. In other words, a human slave, in both Arabic and English languages, is generally under the complete domination of an influence, irrespective of the kind of that influence, another human or anything else.
In all cases, the free will to reverse that influence doesn't exist. This would describe slavery as a degrading and oppressive as it goes against our God given gift of freedom of choice. The loss of our freedom means losing our honor and dignity. Such loss of freedom shatters the divine principal of equality of all humans and further damages the essence of justice which God advocates in all aspects of life. The divine scales of justice mandate that all humans must be justly/equally free to choose, or not, God as the only Divine Authority.
[33:72] We have offered the responsibility (freedom of choice) to the heavens and the earth, and the mountains, but they refused to bear it, and were afraid of it. But the human being accepted it; he was transgressing, ignorant.
It is not a surprise that God's precise and infallible choice of the Arabic words in the Quran perfectly corresponds with the above general understanding and definition of slavery. Our ignorance and narrow vision can throw us off and divert us from the truth, but we cannot go wrong with the flawless, unambiguous Quran. In the following verse, 16:75, we have the divine definition of a slave based on its broad meaning; deprivation of free will:
[16:75] GOD cites the example of a slave who is owned, and is totally powerless, compared to one whom we blessed with good provisions, from which he gives to charity secretly and publicly. Are they equal? Praise be to GOD, most of them do not know.
The above verse is not limiting slavery to the ancient practice of selling/owning humans but rather clearly describes the two components that define slave ; owned and powerless; a person who has no control over his/her life, and has no free will to change his/her oppressive status for reasons that are not detailed in the verse. The fact that Quran is a perpetual, guiding scripture for all generations and civilizations is behind the divine wisdom of not giving any specifics or details about the underlying reasons for losing one's free will. It could be related to addiction of drugs or to economical, social, emotional, mental or physical abuse and oppression. It seems that God deliberately left it opened so that the above definition would be applicable to all styles of slavery and at all times. Based on the above divine definition, if we look around at every corner, we will find a slave waiting to be freed. Quran clearly discourages slavery through the emphasis of freeing slaves whenever possible as a righteous, charitable act and to atone certain offenses.
[2:177] Righteousness is not turning your faces towards the east or the west. Righteous are those who believe in GOD, the Last Day, the angels, the scripture, and the prophets; and they give the money, cheerfully, to the relatives, the orphans, the needy, the traveling alien, the beggars, and to free the slaves; .....
[9:60] Charities shall go to the poor, the needy, the workers who collect them, the new converts, to free the slaves, to those burdened by sudden expenses, in the cause of GOD, and to the traveling alien. Such is GOD's commandment. GOD is Omniscient, Most Wise.
[90:12] Which one is the difficult path?
[90:13] The freeing of slaves.
[4:92] No believer shall kill another believer, unless it is an accident. If one kills a believer by accident, he shall atone by freeing a believing slave, and paying a compensation to the victim's family, unless they forfeit such a compensation as a charity. If the victim belonged to people who are at war with you, though he was a believer, you shall atone by freeing a believing slave. ....
[5:89] GOD does not hold you responsible for the mere utterance of oaths; He holds you responsible for your actual intentions. If you violate an oath, you shall atone by feeding ten poor people from the same food you offer to your own family, or clothing them, or by freeing a slave. ....
[58:3] Those who estrange their wives in this manner, then reconcile thereafter, shall atone by freeing a slave before resuming their sexual relations.....
Even though it is very clear that the practice of slavery goes against the divine system of our freedom and the clear ethical principles of treating one another, we find that God commands us to free slaves rather than directly prohibiting slavery. . God knows that it is very unlikely for slavery to be a discontinued practice on this earth based on the human's aggressive nature and his thirst and passion towards authority, abuse and control. Unrighteousness and greed will always lead to all sorts of socioeconomic injustices and violations of human rights. God has already informed us that this will dominate the earth since the majority of humans are unappreciative and disbelievers. Instead of just prohibiting what He knows will exist irrespective of any divine commands or civil legal systems, God provides us with a realistic and practical approaches to abolish this social disease by constantly freeing slaves and disrupting slavery whenever encountered.. Such approach is also far more effective- instead of just refraining from practicing slavery, as believers, through a direct command, we constantly redeem our souls throughout our journey on earth by freeing the slaves; a non-stop war against slavery waged by those who believe and lead a righteous life. Is GOD not the Most Wise, of all the wise ones (95:8).
Peaceful Friday, salaam and God bless.