Devarim is the last book of the Torah and in general terms it repeats all the essential laws, ideas and history of the first four books. You might well ask why is it necessary to repeat the Torah? There are several answers our rabbis give. Not least is that over the forty-year period different situations and new circumstances required modifications, additions and interpretations. This is all part of the dynamic of Torah. It is never static. Although there was an original Sinai revelation the Torah was and is a living document that calls for a dynamic and creative expansion. Over time this “Oral Law” came to be known as the Talmud and goes on being interpreted to this very day by our Rabbinic experts to meet new conditions (though many still think wrongly that it is fossilized and does not).
But I want to learn something additional. We humans repeat mistakes and fail to learn from history. We need to be reminded over again what the right thing to do is. If only the rest of the world lent the same lesson. How many times have seen that cease fires, concessions to our enemies in the Middle East only increase their hatred and demands for more. The Middle East is not a place that values weakness or even tolerance of different opinions. Islam might have been tolerant in parts once. Some still are. But at this moment the Jihadis have the hearts and minds of the majority and are in a pact of the devil with Left Wing, Liberal westerners.
Devarim reminds us of history. Not to repeat the same mistakes.