This passage is not just slavery, it includes concubinage. Women, all Hebrew women were property in this time period. And I am going to point out that dating does not occur until the last century and of course you remember the women's suffrage movement and the ERA. We are just coming out of this, even Christianity. Paul said there was no difference between male and female but He was slow to show that. Today women are still mostly second rate members in the church. Women pastors...preachers...OH my that from the devil!!!! Things move slow.
Exodus 21:7-11 If a man sells his daughter as a female slave, she is not to go free as the male slaves do. If she is displeasing in the eyes of her master who designated her for himself, then he shall let her be redeemed. He does not have authority to sell her to a foreign people because of his unfairness to her. If he designates her for his son, he shall deal with her according to the custom of daughters. If he takes to himself another woman, he may not reduce her food, her clothing, or her conjugal rights. If he will not do these three things for her, then she shall go out for nothing, without payment of money.
Let me go line by line. While there are different interpretations, I'll give the ones I favor.
Exodus 21:7 And if a man sell his daughter to be a maidservant, she shall not go out as the menservants do.
The source I have says this applied to girls who had not reached puberty yet. The person buying the girl almost surely does so with the prospect of a possible marriage, either to himself or to a son. He would be buying her services for six years only. "Menservants" refers to male "slaves" who were granted liberty if their owners physically damaged them severely. Why make this exemption then? I think so a man who was displeased with a girl couldn't disfigure her as a way of getting rid of her.
8 If she please not her master, who hath betrothed her to himself, then shall he let her be redeemed: to sell her unto a strange nation he shall have no power, seeing he hath dealt deceitfully with her.
In other words, if his intention was to marry her when she was old enough and he changed his mind for some reason, he was not free to sell to foreigners. Since she had worked for so many years, he also could expect the same amount of money he paid for her. Her wages would be deducted from the redemption price. It was also interpreted to mean that her father could not resell her.
Don't forget that a central concept of Judaism is that a man is obliged to make his wife happy. If the man in this case had a girl who displeased him, why did she displease him? Uh, maybe she caused difficulty for him if she was a brute? It would be risky business then to buy a girl for a future marriage unless you were willing to make her happy.
9 And if he have betrothed her unto his son, he shall deal with her after the manner of daughters.
He could not treat her as inferior in any way to other daughters of Israel. He owed her: Clothes, sustenance and sexual relations.
10 If he take him another wife; her food, her raiment, and her duty of marriage, shall he not diminish.
This is more protection for her. He could take another wife if he wanted; but he still had to provide her with food and clothes, and he was expected to give her sexual satisfaction in bed.
11 And if he do not these three unto her, then shall she go out free without money.
In other words, if he didn't treat her with respect, he couldn't claim anyone owed him money even if she hadn't served the full six years. He couldn't divorce her and claim financial damages in court over lost wages owed him.
We may not like the idea of concubinage today; but it existed then, and I see this rule as an effort to limit the harm to women if left unregulated.
Remember too that culture changes; and while the written rules were left unchanged on the books to avoid the idea that people were tinkering with them, the Jews knew that as culture changed, how the rules got applied needed to be changed. Thus there was a need for people educated in the past culture to reinterpret the laws of Moses so they applied to the current time. The average person wasn't expected to understand fully the laws of Moses; they were to supposed to take whatever the Sanhedrin ruled to be right. That's why Jesus told people to obey whatever the Sanhedrin said.
There is one law that was ruled "outdated" completely by the Sanhedrin -- the one about hitting someone with a shoe. It's now forbidden for a man to marry his brother's widow. Synagogues still have silk slippers though just so they can obey that rule. In today's culture, I think something similar could be said that this rule about selling daughters. Most Jews would frown on it, saying that while there is a rule about how it should be done, it's better not to do it at all.
I imagine that in that culture, some families who were very poor might be tempted to do worse things with their daughters if they needed money and having daughters at home was an economic burden. That situation doesn't exist today among Jews, so I'd say the rule became largely irrelevant.
However there are places today in the world where impoverished parents sell their children out of desperation. That "market" is unregulated; and the children often wind up as sex slaves with no rights at all. The laws on the books are impossible to obey for them; if you're desperately poor, some laws can't be obeyed without creating harm of another sort; perhaps laws that permitted them to "sell" them to humane owners might be an improvement. People in the United States would scream bloody murder if Mexico permitted poor parents to sell their children to humane owners who had obligations to fulfill; but they hide their eyes at the fact that much of the prostitution in the United States is the result of poverty in Central America with juveniles forced into it- -- being illegal, it's unregulated and the abuses are worse, it seems to me.
Does this help? Do you want to discuss it, or do you want to tackle another problematical passage?