פרשת ויקהל - פקודי תשכ"ו - פרשת "החודש הזה לכם"

אל הבתים אשר יאכלו אתו בהם ON THE HOUSES WHEREIN THEY SHALL EAT IT — and not upon the lintel and the doorposts which are in the place used for storing straw or in the stalls of oxen, in which people do not live and eat. (Cf. Mekhilta d'Rabbi Yishmael 12:7:2 and הגהות הגר״א thereon).

Rabban Gamliel used to say, "Anyone who has not mentioned these three things on Pesach has not discharged his obligation, and these are [the items that he must mention]: the Pesach sacrifice, matsa and bitter herbs. [The] Pesach [Passover] sacrifice [is offered] - because the Omnipresent passed over the homes of our ancestors in Egypt. Matsa [is eaten] - because our ancestors were redeemed in Egypt. Bitter herbs [are eaten] - because the Egyptians embittered the lives of our ancestors in Egypt." In every generation a person must see himself as though he [personally] had gone out of Egypt, as it is stated, “And you shall tell your son on that day, saying, ‘It is because of what the Lord did for me when I came forth out of Egypt’” (Exodus 13:8). Therefore we are obligated to thank, praise, laud, glorify, exalt, lavish, bless, extol, and adore He Who made all these miracles for our ancestors and for us: He brought us out from slavery to freedom, from sorrow to joy, from mourning to [celebration of] a festival, from darkness to great light, and from servitude to redemption. [Therefore,] let us say before Him, Halleluyah!

על מרורים, “together with bitter herbs.” This was to drive home the memory of the many years their lives had been embittered by the Egyptians. This is why they were not to eat it with something sweet.

For I will go through the land of Egypt in that night, and will smite all the first-born in the land of Egypt, both man and beast; and against all the gods of Egypt I will execute judgments: I am the LORD.

And ye shall observe the feast of unleavened bread; for in this selfsame day have I brought your hosts out of the land of Egypt; therefore shall ye observe this day throughout your generations by an ordinance for ever.

ושמרתם את המצות AND YE SHALL WATCH THE UNLEAVENED BREAD that it shall not reach the stage of becoming leavened; hence the Rabbis said, if it (the dough) is rising (a sign that the leavening process is setting in) she (the woman kneading the dough) polishes it with cold water (i. e. she slaps the dough with hands dipped in cold water). Rabbi Josiah said: Do not read “את המַּצּוֹת”, the unleavened bread, but את הַמִּצְוֹת “[ye shall watch] the commandements” — just as we may not cause the unleavened bread to become leavened by letting the dough remain in its raw state too long so we may not let the commandment become “leavened” by waiting too long before we perform it; but if it (a commandment) comes to your hand, perform it immediately (Mekhilta d'Rabbi Yishmael 12:17:1).

ושמרתם את המצות, to eat them on this day as a memorial. 'כי בעצם היום הזה הוצאתי, וגו, as a result their dough did not have time enough to rise before baking, resulting in it becoming cakes of unleavened bread. It was all due to the haste of being expelled (compare verse 39)

ושמרתם את המצות, “you shall observe the commandment to eat unleavened bread on these days for the future.” We find this formulation being use in this sense also in Numbers 28,2 in connection with the daily communal offering where the Torah writes: תשמרו להקריב לי במועדו, ”make sure that you offer it at the time appointed for it.”