1 Nissan (Rosh Chodesh Nissan)

The first Rashi on Chumash says that really the Torah should have started with Shemos 12- "Hachodesh Hazeh Lachem Rosh Chadashim" (this month should be for you the first month[referring to Rosh Chodesh Nissan]). The reason it doesn't is because this way we can see why we have Eretz Yisrael. Why would we have started from there, there are so many things that we learn from the Torah until there?