The First Ramban

One of the most well-known comments of Rashi is the first one that he makes on Chumash in the name of R' Yitzchak, regarding why HaShem saw fit to begin the Torah with Sefer Bereishis, rather than immediately jumping to the section that discusses the mitzvos that were given to Israel as a nation, which begins with the mitzvah of kiddush ha-chodesh. He answers by citing the passuk from Yeshaya of "Ko'ach ma'asav higid l'amo la-seis lahem nachlas goyim" - "He told the power of His actions to His nation in order to give them the inheritance of nations." In order that the Jews could respond to the complaints of the nations that they had stolen the land from the Canaanites, it was essential that they would have a grasp of the history of the world, so that they would understand that, as the Creator of the world, HaShem had the right to give the different portions of land to whomever he saw fit, and to replace one nation with another over time.

The Ramban asks what seems to be a fundamental question. How could R' Yitzchak countenance the idea that the episode of ma'aseh bereishis could be left out of the Torah? The knowledge that HaShem created the world is one of the principal foundations of Judaism that everything else rests upon. If one lacks this singular point, he possesses nothing.

He answers that the entire first sedra is so filled with deep secrets and allusions that its simple reading is nigh useless in understanding anything about the creation of the world. Rather, everything that we know about the creation of the world is founded in our Oral Tradition. Being that the common people cannot properly understand the method of the creation of the world even with P' Bereishis in place, R' Yitzchak could validly ask why we need it, to which he responded that the illustrated path of history is the primary purpose of the sedra (and the book), not the specific mechanism through which this history unfolded.