The instructions are to Christians. There are no Christians in the Old Testament.
The OT is loaded with slaves.
Scripture uses slaves, freedom, bondage to teach how sin keeps you in bondage, how freedom is in Christ, how one is a servant to who they serve, etc.
Those parallels are spiritual in nature.
You don't have the ability to understand that or what it's teaching.
Yes and so is the New Testament.
Scripture also makes it a point to tell slaves to serve their master as if they were god, in a society that had brutal slavery laws on par with Americas.
It isn’t a metaphor, it is literal and it isn’t purely spiritual slavery. It is literal slavery. There is some scripture like what you are describing mostly calling on people to be “slaves to Christ” or that sin is a kind of moral slavery. But that isn’t what all the scripture is teaching, it is teaching literal rules for being a Christian slave to a master who owns you.
"Obey the government, for God is the One who has put it there. There is no government anywhere that God has not placed in power. So those who refuse to obey the law of the land are refusing to obey God, and punishment will follow."
Slavery was established by the government. It was seen as god’s will and backed up by the Old Testament on rules of taking slaves and how to treat them. There was also two different rules on how to treat slaves, one for the Israelites and one for the canaanites. People on here are conflating the rules for treating Hebrew slaves and the rights of the Israelites in their society with the slavery of non-hebrews which was much more brutal.