Parshat B'Reishit - 5767
The first Rashi in the parsha is relatively famous, as far as Rashis go. The parsha begins in 1:1 by saying "In the beginning Hashem created the heavens and the earth."
Rashi comes along and tells us that the reason the Torah begins with all this history of the world and of the Jewish nation rather than simply beginning with the first mitzva (החודש הזה לכם...), is to let it be known that Hashem created the world and can give the land to whomever He desires. So if/when other nations come to claim the land of Israel from the Jews as having been unfairly captured, the Jews can say God created it and gave it to us, as has clearly been delineated in the Torah that He has the right to do so.
This is a wonderful explanation and should be read in Rashi by everyone. It was clearly written for Jews to internalize the lesson rather than non-Jews, as they likely will not accept such an argument. Rather, we Jews need to internalize the idea that we have the right to the Land of Israel.
However, I would like to offer another suggestion to explain why we begin the Torah reading how Hashem created the world and the history of the world, our forefathers, the Jewish nation, etc.
If the Torah was simply a book compiling all the mitzvos, it is unlikely it would be read by many. Nobody would feel obligated to adhere to the mitzvos and nobody would feel connected to them. Hashem had to begin the book by showing how He created the world, how the forefathers came to recognize Him and commit their lives to His way and how the Jewish nation began and was sustained by Him.
Only after reading all this history and explanation, only after all the raging debates about science and Torah, only after delving into the actual history and stories that made us into the nation we are, only after all that can Hashem delineate the Mitzvos for us. Once we are committed to Hashem and His way, then we can read and study the actual mitzvos and follow and perform them.
Without the history, it is just a bunch of rules nobody would be interested in keeping. The point of the Torah is not just tio give us these rules, but to allow us to dedicate our lives to Hashem. For that we need to mitzvos, but we also need the history.