Why is Pesach 7 days?

Question

Why is Pesach 7 days if the Jews left Egypt on the first day of Pesach?

Looking for answers with sources please- thanks!

Answer 1

This chabad.org provides several reasons, among them:

• 1) Shemos Rabbah 19.7:

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 and thus we are commanded to celebrate those seven days

• 2) Rambam, Moreh Nevuchim 3:43:

The reason for the Passover is well known. It is kept seven days, because the period of seven days is the unit of time intermediate between a day and a month. It is also known how great is the importance of this period in Nature, and in many religious duties.

continuing about why we eat Matzah for 7 days (and by extension, another reason why Pesach is 7 days)

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.