Every year at the Pesach Seder we repeat the words of Rabbi Gamliel from the Haggadah: “What is the reason that we are eating this matza? It is because when G-d redeemed them from Egypt there was not enough time for their dough to rise and become leavened, as it says in the Torah, ‘They baked the dough that they took out of Egypt into unleavened cakes, for they could not become leavened since they were driven from Egypt and they could not delay….’ ”
The first difficulty, according to Abrabanel, is that prior to their hasty exodus G-d had already commanded them to eat matzas and avoid all leavened products. The matzas were to be eaten with bitter herbs along with the sacrificial Pesach lamb on the night before they were to leave Egypt. Why then does Rabbi Gamliel refer only to the unleavened dough that they took with them when they left in haste and not to the matza which they had eaten the night before? Additionally, the verse from the Torah is very enigmatic. What does the Torah mean by “for they could not become leavened?” It would appear that just the opposite would occur. The verse refers to their having reached Succot, their first destination after having left Egypt several days before. Surely the dough would have risen and become leavened during that time. How then could they bake it into "unleavened cakes"?
Abarbanel answers as follows: Rabbi Gamliel is giving the main reason why we eat matza every year at the Seder. However, G-d gave the command to eat matza and refrain from leavened dough before they left Egypt in order to magnify the extent of the sudden and miraculous mass exodus of the entire Jewish population. The people were eager to fulfill the mitzvah of matza and they kneaded the dough under the assumption that they would be able to bake it before leaving Egypt. However, before they could accomplish that, Pharaoh issued the expulsion order and they hastily packed the unbaked dough and carried it on their shoulders. Days later, when they reached Succot, they were able to bake the dough, and although they were afraid that the dough would have become leavened by that time, G-d miraculously intervened and they were still able to bake unleavened matzas from that dough. The entire incident was designed to impress upon them and further generations that the haste with which they left Egypt, and the subsequent miraculous baking of the matzas was an additional demonstration of G-d’s direct hand in all aspects of the exodus from Egypt.
Additionally, G-d commands us to refrain from eating leavened dough for a full seven days in order to further connect us to the miraculous redemption. To refrain from eating leavened products for a day or two would not be a sufficient reminder for later generations of the hasty exodus as it is not at all unusual for people to refrain from such products randomly for short periods of time throughout the year.