"And you shall guard the unleavened breads" (Exodus 12:17). Guard them so that you do not bring them into a state of disqualification. From here the Sages said: if dough is smoothed over with cold water its leaven shall be burned, and one who eats it is exempt [from the penalty of excision]; cracked dough shall be burned, and one who eats it is liable to excision. What is leaven? Dough resembling the horns of locusts. What is cracked dough? Dough whose cracks have run into one another, the words of Rabbi Yehudah. But the Sages say: of both this and that, one who eats it is liable to excision; and what is leaven? Any dough whose surface has turned pale, like a person whose hairs have stood on end. "And you shall guard the unleavened breads." Rabbi Yoshiyah says: Do not read it so, but rather read it 'And you shall guard the commandments' [u-shemartem et ha-mitzvot]. Just as one does not let the matzah go sour, so one should not let the commandments go sour; rather, if a commandment comes to your hand, perform it at once. Rabbi Shimon ben Lakish said: One does not pass over commandments. Rava said: Learn from this teaching of Rabbi Shimon ben Lakish that it is forbidden to move the arm-tefillin past the head-tefillin, and that the clearing of the inner altar precedes the trimming of the five lamps, because whoever enters first encounters the altar. For it has been taught: the table stands in the north, drawn two and a half cubits from the wall, and the menorah in the south, drawn two and a half cubits from the wall, and the altar is centered and stands in the middle.
Guard the Matzot and Do Not Let a Commandment Go Stale
Yalkut Shimoni on Torah 201:6
(שמות יב יז) וּשְׁמַרְתֶּם אֶת הַמַּצּוֹת. שָׁמְרֵם שֶׁלֹּא תְּבִיאֵם לְבֵית הַפָּסוּל. מִכָּאן אָמְרוּ, תִּלְטוֹשׁ בְּצוֹנֵן שְׂאוֹר יִשָּׂרֵף וְהָאוֹכְלוֹ [פָּטוּר, סִידּוּק יִשָּׂרֵף וְהָאוֹכְלוֹ] חַיָּב כָּרֵת. אֵי זֶהוּ שְׂאוֹר, כְּקַרְנֵי חֲגָבִים סִדּוּק, שֶׁנִּתְעָרְבוּ סְדָקִין זֶה בָּזֶה, דִּבְרֵי רַבִּי יְהוּדָה. וַחֲכָמִים אוֹמְרִים, זֶה וְזֶה הָאוֹכְלוֹ חַיָּב כָּרֵת, וְאֵי זֶהוּ שְׂאוֹר, כָּל שֶׁהִכְסִיפוּ פָּנָיו כְּאָדָם שֶׁעָמְדוּ שַׂעֲרוֹתָיו. וּשְׁמַרְתֶּם אֶת הַמַּצּוֹת. רַבִּי יֹאשִׁיָּה אוֹמֵר, אַל תִּקְרֵי כֵּן, אֶלָּא 'וּשְׁמַרְתֶּם אֶת הַמִּצְווֹת', כְּדֶרֶךְ שֶׁאֵין מַחְמִיצִין אֶת הַמַּצָּה כָּךְ לֹא יַחֲמִיצוּ אֶת הַמִּצְווֹת אֶלָּא אִם בָּאָה מִצְוָה לְיָדְךָ עֲשֵׂה אוֹתָהּ מִיָּד. אָמַר רַבִּי שִׁמְעוֹן בֶּן לָקִישׁ, אֵין מַעֲבִירִין עַל הַמִּצְוֹת, אָמַר רָבָא, שְׁמַע מִינָּהּ מִדְּרַבִּי שִׁמְעוֹן בֶּן לָקִישׁ, עִבּוּרֵי דְּרָעָא אֲטוֹטַפְתָּא אָסוּר, וְדִשּׁוּן מִזְבֵּחַ הַפְּנִימִי קוֹדֵם לַהֲטָבַת חָמֵשׁ נֵרוֹת, דְּכִי פָּגַע בְּרֵישָׁא בַּמִּזְבֵּחַ פָּגַע דְּתַנְיָא, שֻׁלְחָן בְּצָפוֹן מָשׁוּךְ מִן הַכֹּתֶל שְׁתֵּי אַמּוֹת וּמֶחֱצָה, וּמְנוֹרָה בְּדָרוֹם מְשׁוּכָה מִן הַכֹּתֶל שְׁתֵּי אַמּוֹת וּמֶחֱצָה, מִזְבֵּחַ מְמֻצָּע וְעוֹמֵד בָּאֶמְצַע.