The last book of the Torah is a sort of last will and testament by Moshe before he dies. It is a repetition of the essential message of the Torah, its laws and the spiritual content of Jewish life.
Moshe starts by describing the sequence of events that led from Egypt to this moment, when, overlooking the Promised Land and knowing that he will not lead the people into it, he prepares the people for the future.
Why the need go over the events that they had lived through? The last time the people were about to invade, forty years earlier, there had been a major crisis. The people were clearly not ready. Moshe wants to make sure that the same thing doesn’t happen this time.
But then why the need to repeat and to add some extra laws that were not mentioned the first time round? One could argue that it was just a matter of emphasis and shifting priorities. In the light of Moshe’s experience over forty years, it is natural that he should focus more on matters of kingship, leadership, organization, and administration than he did in Exodus, when there were other priorities.
There is nothing wrong in shifting emphasis. Consider the phases Judaism has gone through: kings, prophets, and priests. We have worshipped in Tabernacle, Temple, study houses, and synagogues. We have been exiled to the four corners of the earth and lived under different regimes, religions, and cultures. Different aspects of Torah have assumed greater or lesser significance. The crucial issue is that the tradition remains faithful to its essential spiritual and ethical message.
And that is why Moshe keeps on reiterating in his final speeches the importance of the words tzedek (righteousness), tov (good), and yashar (noble), all words which emphasize that, important as the law is, there are moral, ethical values that underpin it, that if we forget them we will have lost our mission and our true soul.