Please be sure to see the key question at the end (it's a real question to you also).
Why didn't God just say: "Stop slavery in all forms, all, now." ?
Why not?
Here's why:
When God did give really basic laws, the 'ten commandments' which are so clear, and
not hard to follow with a bit of will:
Doable Laws:
- Don't murder.
- Don't steal.
- Don't seduce your neighbor's spouse.
- Don't worship idols (and of course, later extra warnings, repeated to say: don't sacrifice your children in fire to idols)
Then the actual outcome was that the Israelites broke these laws over and over and over.
Just over and over.
The old testament is like a lengthy list of examples of them just breaking even
doable laws over and over and over again.
Consider: slavery was a world wide human practice, in all nations practically.
So...do you think a big jump in law,
far past the current culture at that time, a total revolution, all-at-once, could have worked?
What would have happened? Maybe something like Prohibition: increasing disregard for the law everywhere, so that even the rule of law itself becomes weakened also.
To actually do Matthew 7:12 well, consistently...requires something profound to change in the individual.