(1) Observe the month of Aviv and offer a passover sacrifice to your God ה', for it was in the month of Aviv, at night, that your God ה' freed you from Egypt. (2) You shall slaughter the passover sacrifice for your God ה', from the flock and the herd, in the place where ה' will choose to establish the divine name. (3) You shall not eat anything leavened with it; for seven days thereafter you shall eat unleavened bread, bread of distress—for you departed from the land of Egypt hurriedly—so that you may remember the day of your departure from the land of Egypt as long as you live. (4) For seven days no leaven shall be found with you in all your territory, and none of the flesh of what you slaughter on the evening of the first day shall be left until morning.
Why Do We Eat Matzah in the Spring? by Dr.Yael Avrahami from thetorah.com
In the Levant, two harvest seasons followed one after another, the barley harvest and then the wheat harvest. In the Gezer Calendar’s list of seasons, for instance, the month of harvesting barley (ירח קצר שערם) is followed by “the month of harvesting and measuring” (ירח קציר וכל), which must refer to the wheat harvest; as the most important crop, the wheat harvest was designated through the general term of “harvesting.”...
As the festival of Qatzir (or Shavuot) marks the wheat harvest (Exod 34:22), Matzot, which comes a few weeks before, marks the barley harvest.
In fact, the simple meaning of the word matzah, the eating of which is this holiday’s central ritual, is barley flatbread. Barley was generally not leavened with yeast since the main benefit of such leavening is to make the dough rise and produce a loaf, but this cannot be done with barley, which only yields flatbreads...
Despite its connection to barley, I would argue that the Festival of Matzot was not primarily a celebration of the barley harvest. Instead, its rituals are focused on the upcoming wheat harvest.
During the early spring, when barley was ripe and ready for baking into flatbreads, the unripe, green ears of wheat would begin to appear. The word in Hebrew for these green ears is “aviv” (אביב), and the Torah more than once emphasizes that the festival of Matzot should take place “in the month of Aviv,” i.e., “the month the green (unripe) ears [of wheat].”
The aviv period of wheat lasts a number of weeks and thus, while the Israelites waited for the new wheat to fully ripen and then dry, they could supplement their diet of barley flatbreads with this unripe, green wheat...
I suggest, therefore, that the practice of not eating bread during this period even in years of plenty, and instead eating only matzot, was meant to mark the liminal period between the end of the barley harvest and the beginning of the wheat harvest...
Until about 150 years ago, the standard way of leavening bread was by using a starter from previously fermenting dough (sourdough), a process first discovered in Egypt about 6000 years ago. Sourdough is produced through natural fermentation, when flour and water are exposed to yeast as well as what today we recognize as lactobacilli bacteria.
It takes about a week for flour and water set outside to absorb enough naturally occurring yeast to rise; this is a long time to wait for bread. For this reason, sourdough, already fermented dough, was kept and used to ferment the next batch of dough much more quickly.
According to the Torah’s commandment to remove all leavening agents from one’s home, the Israelites would have had to destroy their supply of sourdough and start the process of fermentation all over again from scratch with the new wheat.
Privation Ritual
Starting fresh by destroying all leavening agents and eating only barley flatbreads until the next wheat harvest did more than just mark the new year, it also functioned as a privation ritual, in which the Israelites would mimic the practice of a bad year by living as if they had no wheat in stock. Doing so was a way of ritually ensuring that the wheat harvest would also go “properly,” and the coming year’s bread supply would be secure.
Enacting a small amount of controlled privation or destruction is a standard element of protection rituals, a classic example being the requirement to “afflict oneself” on Yom Kippur to avoid further divine punishments.
(ה) אֵלּוּ דְבָרִים שֶׁאָדָם יוֹצֵא בָהֶן יְדֵי חוֹבָתוֹ בְּפֶסַח, בְּחִטִּים, בִּשְׂעוֹרִים, בְּכֻסְּמִין וּבְשִׁיפוֹן וּבְשִׁבֹּלֶת שׁוּעָל...
(5) These are the types of grain with which a person fulfills their obligation to eat matza on the Passover: With wheat, with barley, with spelt [kusmin], with rye [shifon], and with oats [shibbolet shu’al]...
אָמַר רַבִּי שִׁמְעוֹן בֶּן לָקִישׁ, וְכֵן תָּנָא דְּבֵי רַבִּי יִשְׁמָעֵאל, וְכֵן תָּנָא דְּבֵי רַבִּי אֱלִיעֶזֶר בֶּן יַעֲקֹב: אָמַר קְרָא ״לֹא תֹאכַל עָלָיו חָמֵץ שִׁבְעַת יָמִים תֹּאכַל עָלָיו מַצּוֹת״. דְּבָרִים הַבָּאִים לִידֵי חִימּוּץ — אָדָם יוֹצֵא בָּהֶן יְדֵי חוֹבָתוֹ בְּמַצָּה...
Rabbi Shimon ben Lakish said, and likewise a Sage of the school of Rabbi Yishmael taught, and likewise a Sage of the school of Rabbi Eliezer ben Ya’akov taught that the verse states: “You shall eat no leavened bread with it; seven days you shall eat with it matza” (Deuteronomy 16:3), i.e. substances which will come to a state of leavening, a person fulfills their obligation to eat matza with them...
On Pesach, it is forbidden to derive any benefit from chametz, as [Exodus 13:3] states: "Do not eat (לא יאכל) chametz"; i.e., it is not permitted [to be used to derive benefit that leads to] eating.
A person who leaves chametz within their property on Pesach, even though they do not eat it, transgresses two prohibitions: [Exodus 13:7] states: "No leavening agent may be seen in all your territory" and [Exodus 12:19] states: "No leavening agent may be found in your homes."
[Though the prohibitions stated in these verses apply to שאור,] it is the same prohibition which forbids both חמץ (leaven) and שאור (a leavening agent).
The Sages forbade the eating of chametz from the beginning of the sixth hour in order to prevent infringement upon a Torah commandment. Thus, from the beginning of the sixth hour, it is forbidden to eat or benefit from chametz, based on Rabbinic law. During the rest of the day, from the seventh hour on, eating chametz is forbidden because of the Torah law.
During the fifth hour of the day, we do not eat chametz, lest the day be cloudy and we err between the fifth and six hours. However, there is no prohibition against benefiting from chametz during the fifth hour.
What is the destruction to which the Torah refers? to nullify chametz within your heart and to consider it as dust, and to resolve within your heart that you possesses no chametz at all: all the chametz in your possession being as dust and as a thing of no value whatsoever.
כֵּיצַד בִּעוּר חָמֵץ. שׂוֹרְפוֹ אוֹ פּוֹרֵר וְזוֹרֶה לָרוּחַ אוֹ זוֹרְקוֹ לַיָּם. וְאִם הָיָה הֶחָמֵץ קָשֶׁה וְאֵין הַיָּם מְחַתְּכוֹ בִּמְהֵרָה הֲרֵי זֶה מְפָרְרוֹ וְאַחַר כָּךְ זוֹרְקוֹ לַיָּם... נְתָנוֹ לְעַכּוּ''ם קֹדֶם שָׁעָה שִׁשִּׁית אֵינוֹ צָרִיךְ לְבָעֵר...
How must chametz be destroyed? It may be burned; crumbled and tossed to the wind; or thrown into the sea. If the chametz is hard and the sea will not cause it to dissolve speedily, one should crumble it and then throw it into the sea...
A person who gave it to a gentile before the sixth hour need not destroy it...
אִיכָּא דְאָמְרִי, הָא רַב הַמְנוּנָא מְצַלֵּי לַהּ. וְרַבִּי אָלֶכְּסַנְדְרִי בָּתַר דִּמְצַלֵּי אָמַר הָכִי: ״רִבּוֹן הָעוֹלָמִים, גָּלוּי וְיָדוּעַ לְפָנֶיךָ שֶׁרְצוֹנֵנוּ לַעֲשׂוֹת רְצוֹנֶךָ, וּמִי מְעַכֵּב? — שְׂאוֹר שֶׁבָּעִיסָּה וְשִׁעְבּוּד מַלְכֻיוֹת. יְהִי רָצוֹן מִלְּפָנֶיךָ שֶׁתַּצִּילֵנוּ מִיָּדָם, וְנָשׁוּב לַעֲשׂוֹת חוּקֵּי רְצוֹנְךָ בְּלֵבָב שָׁלֵם״.
Some say that... after Rabbi Alexandri prayed, he would say the following: Ruler of the Universe, it is revealed and known before You that our will is to perform Your will, and what prevents us? the yeast in the dough, and the subjugation to the kingdoms. May it be Your will that You will deliver us from their hands, so that we may return to perform the edicts of Your will with a perfect heart.
ולא יאכל חמץ... דמצה אין בה יתרון ע״י תחבולות ידי האדם להעלות העיסה יותר מהקמח והמים שנבראים ממנו ית׳. משא״כ חמץ שולט בם תחבולות האדם להעלות העיסה ע״י שאור מש״ה הוא אות שקיום ישראל הוא רק ברוח ה׳...
"LEAVEN MAY NOT BE EATEN (on Passover) ... matza takes no advantage of the human technological ingenuity and creativity which allows man to raise the dough more than simple flour and water which are created by God. Chametz is the epitome of human involvement in nature. Thus, non-leaven is the symbol of the survival and ongoing existence of the Jewish People as they survive solely through the spirit of God."
The Symbolism of Chametz by Rabbanit Gloria Nusbacher
According to Rav Ezra Bick, a Ram at Yeshivat Har Etzion, the Torah’s linking of Pesach and Shavuot through the counting of the omer clearly indicates that Pesach starts a process that culminates in Shavuot:
“Pesach, the holiday of freedom, is directed toward the goal of Shavuot, the day of the giving of the Torah. Freedom is the necessary prerequisite for responsibility and obligation, and, conversely, is meaningless without a goal to which one is committed.”
Rav Bick sees the treatment of chametz as part of the process of moving from Pesach to Shavuot. He posits that the process of leavening represents the realization and expression of a hidden potential:
“Matza is simply flour and water, baked. Bread is made of the same ingredients, but when you leave it around, unwatched and unbothered, it magically rises and grows, realizing a hidden potential and expressing it.”
According to him, by forbidding chametz on Pesach, the Torah is warning us that
“[t]he raw powers of the human spirit, unguided and unchannelled, are anarchic precisely because they are powerful,precisely because they represent real growth and vitality. The first step, when granted freedom, is not to run and let all the repressed inclinations and urges fly out. Even then–ESPECIALLY THEN–one should eat matza and beware the hidden powers bursting to be free.”
Rather, we need seven weeks of counting the days toward the giving of the Torah, during which time we can begin to understand the purpose of freedom and acquire a structure to channel our potential. Only at the end of such a period can our raw potential be transformed into creativity in service to God. Attaining such a level of development is reflected by bringing an offering of chametz.
I think there is an alternative way to see the symbol of chametz in context of the process of moving from Pesach to Shavuot. I see chametz as a symbol of pride, which the newly-freed slaves were sorely lacking. The matza they ate was indeed lechem oni, the bread of affliction, reflecting the mental condition of a downtrodden and demoralized people, who were likely in a state of shock at the moment of freedom. This is not a state in which it is possible to meaningfully serve God. The seven weeks between Pesach and Shavuot represent the time needed to develop the sense of pride and self-confidence that is necessary in order to receive the Torah and enter into covenant with God. The requirement of bringing a korban of chametz on Shavuot reflects the importance of these developed traits.