Quite simply, the Torah itself tells us on numerous occasions that we are to celebrate Passover for seven days.1 (Outside of Israel, we celebrate for eight days, for reasons outlined here.)

The question is, why?

Out of Danger

The Midrash explains that although the Jews left Egypt on the first day of Passover, they were pursued by the Egyptians until the parting of the Red Sea, which occurred seven days later. Thus, although the Exodus started on the first day, it was not completed until the seventh day. We are commanded to celebrate those seven days.2

Seven Days of the Week

The same Midrash also connects the seven days of Passover to the seven days of the week.

In the words of the Midrash:

“No leavened bread shall be seen with you for seven days,” corresponding to the seven days between the redemption [from Egypt] and the dividing of the Red Sea. Just as there were seven days of creation at the beginning, and just as the Sabbath is observed at the end of seven days, so shall these seven days be kept each year.3

Some explain the connection between the seven days of Passover and the seven days of creation thus: Just as without G‑d’s creating the world it would not exist, so too, without the Jews being redeemed from Egypt and ultimately receiving the Torah, the world would have ceased to exist, as the purpose of creation would not have been realized.4

Like the Shabbat

The Lubavitcher Rebbe, Rabbi Menachem Mendel Schneerson, of righteous memory, explains (based on Maimonides’ Mishneh Torah5) that if you analyze the words of the Midrash you will see that it is conveying a profound lesson, which has halachic ramifications.

There is a mitzvah to remember the Exodus every day—not just on Passover. However, the “remembrance” that we are enjoined to do on Passover is very different from what we do daily. Remembering that “G‑d took us out of Egypt” can suffice for the daily mitzvah. But when it comes to Passover, the remembrance needs to be of a different quality.

For example, there is a mitzvah to remember Shabbat. Although we keep Shabbat by abstaining from doing forbidden work (i.e., abstaining from the negative), the main way of remembering and sanctifying the Shabbat is through doing the positive actions: lighting candles, resting, making kiddush and having a festive meal. So too, when it comes to Passover, the mitzvah of remembering the Exodus is not simply to stress the removal of the negative, the fact that we were taken out of slavery in Egypt. But on the positive side, we should stress the miracles that G‑d performed and the “essential freedom” we achieved through the Exodus on Passover, which transformed the essential nature of the Jewish people.

The miracle is not just that we are no longer slaves. After all, we have been oppressed under many other tyrants since the Exodus. Rather, the greatness of the Exodus is that we acquired the nature of free people, to the point that in our essence we are free, and no one has the ability to subjugate our essential selves ever again. For even if they attempt to conquer our physical bodies, they don’t have the ability to enslave our spirit.6

Not a Fluke

Maimonides in his Guide for the Perplexed explains that if we were to just eat matzah for a few days, it may not be discernible that we are doing it for a mitzvah. After all, it frequently happens that a person may eat a certain type of food for two or three days. But by our continuing to eat matzah for a period of seven days—a complete unit in time—it is clear and publicized that we are doing it because of the mitzvah.7

Imbuing Time with Holiness

Some explain that seven days—a full week—is considered a complete unit of natural time. We celebrate for seven days to perfect nature and infuse it with holiness.8

Eating Matzah for Seven Days

Many commentaries point out that even before the Exodus, the Jews were commanded to eat matzah on the night they left Egypt. But that command was in effect for only one day, and after that they were technically permitted to eat regular bread. But since they left Egypt in a hurry (and continued to rush until the Egyptians were finally neutralized seven days later), they ate fast-baking matzah for seven days. It was for this reason that G‑d commanded subsequent generations to abstain from chametz and eat matzah for all seven days.9 (For more on this, see Why Do We Eat Matzah on Passover?)

Seven Attributes

The Kabbalists explain that the service of a baal teshuvah (one who repents and returns to G‑d) results in a supra-rational revelation of G‑dly energy. After all, the natural order of things is that crime results in punishment. In order for G‑d to forgive, He rises above the natural cycle.

In the created order, the Divine energy comes through the seven attributes (kindness, severity, etc.). When G‑d circumvents the natural order, as it were, the result is something above and beyond the seven attributes.

Rabbi Schneur Zalman of Liadi explains that Passover and Sukkot, which are both celebrated for seven days, represent the natural order. Shavuot, on the other hand, comes after 49 days of the Omer, in which we work on refining ourselves, attaining the status of a baal teshuvah. The result is a revelation that is above the regular order of the world, so it is a one-day holiday.

Conversely, Passover, when we have no chametz (which personifies ego), represents the service of the tzaddik. Thus, it results in an “orderly revelation,” which is revealed through the seven attributes. This is reflected in a seven-day holiday.10