First, in Yitro, there were the Aseret Hadibrot, the “ten utterances” or general principles. Now in Mishpatim come the details. Here is how they begin:

If you buy a Hebrew servant, he is to serve you for six years. But in the seventh year, he shall go free, without paying anything . . . But if the servant declares, ‘I love my master and my wife and children and do not want to go free,’ then his master must take him before the judges. He shall take him to the door or the doorpost and pierce his ear with an awl. Then he will be his servant for life. (Ex. 21:2-6)

There is an obvious question. Why begin here? There are 613 commandments in the Torah. Why does Mishpatim, the first law code, begin where it does?

The answer is equally obvious. The Israelites have just endured slavery in Egypt. There must be a reason why this happened, for God knew it was going to happen. Evidently, He intended it to happen. Centuries before He had already told Abraham it would happen:

As the sun was setting, Abram fell into a deep sleep, and thick and dreadful darkness came over him. Then the Lord said to him, “Know for certain that for four hundred years your descendants will be strangers in a country not their own and that they will be enslaved and mistreated there. (Gen 15:12-13)

It seems that this was the necessary first experience of the Israelites as a nation. From the very start of the human story, the God of freedom sought the free worship of free human beings, but one after the other people abused that freedom: first Adam and Eve, then Cain, then the generation of the Flood, then the builders of Babel.

God began again, this time not with all humanity, but with one man, one woman, one family, who would become pioneers of freedom. But freedom is difficult. We each seek it for ourselves, but we deny it to others when their freedom conflicts with ours. So deeply is this true that within three generations of Abraham’s children, Joseph’s brothers were willing to sell him into slavery: a tragedy that did not end until Judah was prepared to forfeit his own freedom that his brother Benjamin could go free.

It took the collective experience of the Israelites, their deep, intimate, personal, backbreaking, bitter experience of slavery – a memory they were commanded never to forget – to turn them into a people who would no longer turn their brothers and sisters into slaves, a people capable of constructing a free society, the hardest of all achievements in the human realm.

So it is no surprise that the first laws they were commanded after Sinai related to slavery.

It would have been a surprise had they been about anything else. But now comes the real question. If God does not want slavery if He regards it as an affront to the human condition, why did He not abolish it immediately? Why did He allow it to continue, albeit in a restricted and regulated way? Is it conceivable that God, who can produce water from a rock, manna from heaven, and turn the sea into dry land, cannot change human behavior? Are there areas where the All-Powerful is, so to speak, powerless?

In 2008 economist Richard Thaler and law professor Cass Sunstein published a fascinating book called Nudge. In it, they addressed a fundamental problem in the logic of freedom. On the one hand, freedom depends on not over-legislating. It means creating space within which people have the right to choose for themselves.

On the other hand, we know that people will not always make the right choices. The old model on which classical economics was based, that left to themselves people will make rational choices, turns out not to be true. We are deeply irrational, a discovery to which several Jewish academics made major contributions. The psychologists Solomon Asch and Stanley Milgram showed how much we are influenced by the desire to conform, even when we know that other people have got it wrong. The Israeli economists, Daniel Kahneman, and Amos Tversky, showed how even when making economic decisions we frequently miscalculate their effects and fail to recognize our motivations, a finding for which Kahneman won the Nobel Prize.

How then do you stop people doing harmful things without taking away their freedom? Thaler and Sunstein’s answer is that there are oblique ways in which you can influence people. In a cafeteria, for example, you can put healthy food at eye level and junk food in a more inaccessible and less noticeable place. You can subtly adjust what they call people’s “choice architecture.”

That is exactly what God does in the case of slavery. He does not abolish it, but He so circumscribes it that He sets in motion a process that will foreseeably, even if only after many centuries, lead people to abandon it of their own accord.

A Hebrew slave is to go free after six years. If the slave has grown so used to his condition that he wishes not to go free, then he is forced to undergo a stigmatizing ceremony, having his ear pierced, which thereafter remains as a visible sign of shame. Every Shabbat, slaves cannot be forced to work. All these stipulations have the effect of turning slavery from a lifelong fate into a temporary condition, and one that is perceived to be a humiliation rather than something written indelibly into the human script.

Why choose this way of doing things? Because people must freely choose to abolish slavery if they are to be free at all. It took the reign of terror after the French Revolution to show how wrong Rousseau was when he wrote in The Social Contract that if necessary people have to be forced to be free. That is a contradiction in terms, and it led, in the title of J. L. Talmon’s great book on the thinking behind the French revolution, to totalitarian democracy.

God can change nature, said Maimonides, but He cannot, or chooses not to, change human nature, precisely because Judaism is built on the principle of human freedom. So He could not abolish slavery overnight, but He could change our choice architecture, or in plain words, give us a nudge, signaling that slavery is wrong but that we must be the ones to abolish it, in our own time, through our own understanding. It took a very long time indeed, and in America, not without a civil war, but it happened.

There are some issues on which God gives us a nudge. The rest is up to us.

For more from Rabbi Sacks, please visit www.rabbisacks.org