Also, how do you explain God being okay with slavery but its now something that's becoming less acceptable as humanity develops?
A few things here. One is that slavery in the OT was different to slavery in the modern world. There was no income support supplied by the government, and no way to house and feed people who could not do this for themselves. As a result, many people opted to be a slave voluntarily so they could have a better life. They were not kidnapped, and received food and shelter in exchange for labour. God did not condone it, but made some rules about it, rules in favour of the slave.
You can't kidnap a person to make them your slave
"He who kidnaps a man, whether he sells him or he is found in his possession, shall surely be put to death." (Exodus 21:16)
You must preserve their life
"If a man strikes his male or female slave with a rod and he dies at his hand, he shall be punished." (Exodus 21:20)
If you injure your slave you must set them free
"If a man strikes the eye of his male or female slave, and destroys it, he shall let him go free on account of his eye. "And if he knocks out a tooth of his male or female slave, he shall let him go free on account of his tooth." (Exodus 21:26-27)
They must have a day of complete rest, every week
"Six days you are to do your work, but on the seventh day you shall cease from labor so that your ox and your donkey may rest, and the son of your female slave, as well as your stranger, may refresh themselves. (Exodus 23:12)
You must not speak evil of a slave
Do not slander a slave to his master, Or he will curse you and you will be found guilty. (Proverbs 30:10)
"You shall not hand over to his master a slave who has escaped from his master to you. (Deuteronomy 23:15)
You must be kind towards your slave
'If a countryman of yours becomes so poor with regard to you that he sells himself to you, you shall not subject him to a slave's service. 'He shall be with you as a hired man, as if he were a sojourner; he shall serve with you until the year of jubilee. 'He shall then go out from you, he and his sons with him, and shall go back to his family, that he may return to the property of his forefathers. 'For they are My servants whom I brought out from the land of Egypt; they are not to be sold in a slave sale. 'You shall not rule over him with severity, but are to revere your God. (Leviticus 25:39-43)
You must provide a way out of slavery, should they choose it
"If you buy a Hebrew slave, he shall serve for six years; but on the seventh he shall go out as a free man without payment." (Exodus 21:2)
Treat your slaves like your family
He who pampers his slave from childhood Will in the end find him to be a son. (Proverbs 29:21)
Always be fair to your slave
Masters, grant to your slaves justice and fairness, knowing that you too have a Master in heaven. (Colossians 4:1)
The thing about the Christian life is that, the more you learn and align yourself with God, the more your old man will be removed and the new man will be put on. So over time, the fruits of the spirit, peace, love, joy, gentleness, meekness, kindness, will be reflected in the person so as to mirror God more. This then impacts on human relationships, such as work colleagues, family, or in this case, slavery.
God makes it clear, Whether slave or free, he views them the same. Completely equal.
There is neither Jew nor Greek, there is neither slave nor free man, there is neither male nor female; for you are all one in Christ Jesus. (Galatians 3:28)
knowing that whatever good thing each one does, this he will receive back from the Lord, whether slave or free. (Ephesians 6:8)
And masters, do the same things to them, and give up threatening, knowing that both their Master and yours is in heaven, and there is no partiality with Him. (Ephesians 6:9)
a renewal in which there is no distinction between Greek and Jew, circumcised and uncircumcised, barbarian, Scythian, slave and freeman, but Christ is all, and in all. (Colossians 3:11)