Exodus 21:23-27

God's underlying basis for dealing with sin is by the principle of proportionate punishment, in which the punishment fits the crime:

The principle here was that the punishment must match, but not exceed, the damage done. There was a strict limit on the amount of damages anyone could collect. In modern terms it might read: car bumper for car bumper or window for window. No one was to try to get rich off such situations.

Also, this was to be a rule of thumb for the judges, not an authorization of personal vendetta or private retaliation. So there are greater and lesser punishments for greater and lesser sins.

Exodus 21:26-27

This shows us that any slave who suffered permanent injury as a result of his owner's or employer's negligence or discipline beyond the bounds of correctness, the slave was immediately free. This law was given to make slave owners think twice before using abusive tactics lest he lose his financial investment in the slave. This set Israel's slavery laws above every other nation. The slave had rights. He was born in the image of God too.