Deuteronomy 15:12-23 - Rights for Slaves

The releasing if debts applied to slaves as well. Sometimes people object to the use of slavery in Israel. However, compared to other nations the rules on slaves were amazingly liberal. Slaves were to be released in the seventh year, and they were to be given gifts. This was no normal treatment of slaves! And while we get on our high horse about slavery we do well to remember that slavery still exists even in our own country. There are sex slaves, and there is exploitation of migrant workers. You can probably also make a case that we exploit workers in third world countries. Time spent criticising slave conditions in Old Testament Israel would be far better spent learning from the Law and putting our own house in order.

The reason for the command on good treatment of slaves was that Israel had been in slavery herself once, and that God had blessed them.

If a slave liked his owners (in fact the word servant is used here) he could stay with them. Now he would only want this if he was treated well. 

The natural reaction may be that all this "slaves rights" nonsense would be far too costly. God rejects this attitude. They were not to consider it a hardship, and indeed the Lord would bless them.

God's economy works on very different principles to the world's economy, and it results in freedom and prosperity, not slavery and poverty.
The firstborn of their flocks were to be dedicated to the Lord, this was because the Lord had saved the people form the plague of the firstborn in Egypt.