(14) This day shall be to you one of remembrance: you shall celebrate it as a festival to the Lord throughout the ages; you shall celebrate it as an institution for all time.
(15) Seven days you shall eat unleavened bread; on the very first day you shall remove leaven from your houses, for whoever eats leavened bread from the first day to the seventh day, that person shall be cut off from Israel.
(16) You shall celebrate a sacred occasion on the first day, and a sacred occasion on the seventh day; no work at all shall be done on them; only what every person is to eat, that alone may be prepared for you.
(17) You shall observe the [Feast of] Unleavened Bread, for on this very day I brought your ranks out of the land of Egypt; you shall observe this day throughout the ages as an institution for all time.
(18) In the first month, from the fourteenth day of the month at evening, you shall eat unleavened bread until the twenty-first day of the month at evening.
(19) No leaven shall be found in your houses for seven days. For whoever eats what is leavened, that person shall be cut off from the community of Israel, whether he is a stranger or a citizen of the country.
(20) You shall eat nothing leavened; in all your settlements you shall eat unleavened bread.
(14) This day shall be to you one of remembrance: you shall celebrate it as a festival to the Lord throughout the ages: Here the text transitions from the specific requirements of “the Egyptian Passover” – taking the lamb in advance, smearing the lintel with blood, girding the loins, etc. – to a description of how “Passover for the generations” is to be observed.
You shall celebrate it as an institution for all time: Vivid narratives are a prerequisite for creating an enduring national consciousness. The Exodus would become one of many such stories in the future, and to that end, the plagues had to be colorful and develop gradually. The Passover festivities are unusually dramatic, and the Exodus itself was “hurried.”
(15) Seven days you shall eat unleavened bread: The Passover celebration, which begins with sacrificing of the Paschal lamb on the eve of the holiday, and consuming it on the first night, then continues with eating matzah all seven days. Because matzah is eaten along with the Passover sacrifice (v.8), continuing to eat matzah throughout all of Passover further creates an “aftertaste” to that sacrifice.
Whoever eats leavened bread – that person shall be cut off from Israel: Not only in the sense that the Almighty will cut him off from his people, for he is himself the cause of that excision as well. The Exodus establishes the purpose and meaning of the Jewish people’s existence. A Jew who eats leaven on Passover denies this purpose and meaning, and therefore ceases to be part of the Jewish nation, and is exterminated from its midst.
(16) You shall celebrate a sacred occasion on the first day, and a sacred occasion on the seventh day: As it later turns out, the observance of the first day of Passover as a “sacred occasion” is a remembrance of the Exodus itself, while the last (seventh) day recalls the crossing of the Red Sea, which, according to tradition, occurred on the seventh day following the Exodus. But the Passover laws of this passage establish these “sacred occasions” in advance. That is, events as they will eventually develop are foreseen by the Torah even before they actually occur.
No work at all shall be done on them: To this extent, the Jewish festivals are like the Shabbat (Sabbath) that the Jews observe each and every Saturday.
Only what every person is to eat, that alone may be prepared for you: But the laws of the Jewish festivals are more lenient than those of Shabbat, in that it is permitted to cook on the festivals. There are two main reasons for this leniency:
- While the central theme of Shabbat is rest, the idea of the festivals is different – they are meant to afford enjoyment and pleasure. Tasty, freshly prepared food is important for achieving that.
- Shabbat commemorates the Creation (Gen. 2:3, Exod. 20:11, 31:17), in which humans did not participate, whereas Passover and the other festivals commemorate the Exodus and other events in Jewish history, in which the Jewish people were directly involved. The observance of Shabbat therefore demands greater passivity, while the festivals allow, and indeed require, a certain level of activity.
(19) No leaven shall be found in your houses for seven days. For whoever eats what is leavened, that person shall be cut off from the community of Israel, whether he is a stranger or a citizen of the country: One of Egyptian civilization’s outstanding achievements was the invention of leavened bread, which made it possible to create reserves of food for long-term storage. Upon leaving Egypt, the Jewish nation declares a clean break with the civilization that gave rise to it, but at the same time, Israel inherits Egypt’s achievements. The abstention from leavened bread, which demonstrates Jewish independence from Egyptian civilization, therefore lasts only one week, while during the rest of the year Israel may benefit from Egypt’s achievements.
 Leavened bread allows us to make crackers – a ready-to-eat food that can be stored for the long term. Those cannot be made from unleavened dough, because the final product becomes inedible once it completely dries out. Modern, long-stored (thinly rolled) matzah was first produced only in the Middle Ages. Until then matzah looked like ordinary flat cakes, and was always baked shortly before being eaten (except on Shabbat, of course).