In this week's parsha, we see a group of three angels being treated to two different feasts. At one, Sara baked cakes, but they might not have been set out. At another, the guests were given matza. Why, one might ask? Because it was Pesach.
Really. According to Rav Bechaye, the commemoration of the Exodus accounts for both the unserved cakes (Sara let the dough sit too long and it became chametz) and Lot's matzas. Never mind that the specific incident that would trigger the celebration of Pesach, and the commandment to avoid all things chametz during that time were A COUPLE OF CENTURIES AWAY!
And here we come to the biggest problem I have with Midrash--the Torah existed before it was written.
Really, if we had enough foresight to know that we would have to eat matza for a week in the spring to commemorate our freedom from Egyptian slavery, then why didn't we have the foresight to get out of Dodge before it became an issue? Why did we stay after Joseph died? Why go to Egypt in the first place? Why not stay in Canaan and keep our freedom, thus avoiding the need to commemorate a Biblical feast hundreds of years before it was necessary?