Exode 12:8

And you shall eat the flesh on that night, the fifteenth of Nisan, until the dividing of the night roasted with fire, without leaven, with horehound and lettuce shall you eat it.

AND UNLEAVENED BREAD, ‘AL’ (WITH) BITTER HERBS THEY SHALL EAT IT. The purport of the verse is as follows: And they shall eat the flesh in that night, roast with fire, and with unleavened bread with bitter herbs, they shall eat it. [The word al here thus means “with,” and not “upon,” as it generally does.] Similarly: ‘al’ unleavened bread and bitter herbs means “with”; And they came both men ‘al’ women [means “with” the women]; its head ‘al’ its legs ‘v’al’ the inwards thereof [means its head “with” its legs “and with” the inwards thereof]. Scripture does not say im (with) [but instead uses al] in order to instruct that it is not obligatory to wrap them together, [i.e., insert the paschal meat and the bitter herbs between the unleavened bread], and eat them. on the night of Passover, the wrapping together of unleavened bread and bitter herbs is observed “according to the custom of Hillel.” Thus [the word umatzoth (and unleavened bread)] is missing the letter beth, [which would make it ubematzoth (and with unleavened bread)], similar to the expressions: they shall wash ‘mayim’ (water) [the word missing a beth, which would make it b’mayim, (with water)]; And Seled died ‘lo’ (no) children, [the word lo missing a beth, which would make it b’lo (without) children]. Thus Scripture teaches that there is no commandment for eating the bitter herbs alone, but only with the eating of the flesh of the Passover-offering. (Mishneh Torah, Hilchoth Chametz Umatzah, 7:12). Concerning unleavened bread, however, Scripture repeated it by commanding, At even ye shall eat unleavened bread, even by itself [when there is no Passover-offering], as is the opinion of our Rabbis.
A more correct interpretation is that we say that the word, umatzoth (and unleavened bread), is connected with the earlier part of the verse: And they shall eat the flesh … and unleavened bread. The verse then continues to command that the flesh mentioned be eaten with bitter herbs. Thus He commanded the eating of the flesh with the eating of the unleavened bread, but He did not command the eating of bitter herbs, except by saying that they should eat the meat with bitter herbs, thus hinting that there is no [separate] commandment regarding the bitter herbs. It is only that the meat must be eaten with them, and when there is no Passover-offering there is no specific commandment [of the Torah] regarding the eating of the bitter herbs. It also teaches us that the bitter herbs do not invalidate the meat. Thus, if one ate the meat of the Passover-offering and did not eat bitter herbs, he has [nevertheless] fulfilled his duty of eating the Passover-offering, since the commandment concerning the eating of the Passover-offering is like the commandment of eating unleavened bread, each one an independent commandment in itself.

'ואכלו את הבשר בלילה הזה צלי אש וגו, every reference to the eating of this meal reflects the haste with which it had to be consumed.

ואכלו את הבשר, “they are to eat the meat;” this is the reason why the people established the custom to take three unleavened loaves of bread on the evening when the meat of the Passover would be consumed. It was a reminder of the three measures of flour Avraham told Sarah to use when baking cakes for what turned out to be the three angels, one of whom predicted when she would give birth to Yitzchok. (Genesis 18,6) The date happened to be that of the first day of Passover, (in the future) as we know from the fact that on the same evening Lot welcomed two of these angels and served them unleavened bread. An alternate version of the significance of the three matzot on our seder dish is that they are to remind us of the three patriarchs. The reason why we break the middle one of these three matzot in half is that it symbolises G–d having split the sea of reeds in half to enable the Jewish people to cross it and escape the pursuit of Pharaoh and his army. We pronounce the special blessing over one half of this middle matzah, as related in the Talmud tractate Pessachim folio 115, as a reminder that it is called the “bread of the poor,” meaning that a poor man does not have a whole loaf of bread at his disposal. The reason why we perform two “dippings” on that night is to serve as a reminder that when becoming officially Jewish after performing the circumcision, both the people themselves and their slaves immersed themselves in a ritual bath. An alternate interpretation is that we had to dip the blood of the Paschal lamb and sprinkle it on the lintel and upright posts, mezuzot, of our homes, to insure that the firstborn Jews would not be killed on that night, as were those of the Egyptians. We recite a further reminder of this by quoting from the Book of Ezekiel, that our redemption was linked to our being kept alive by offering that blood (Ezekiel 16,6). One of the reasons why this ritual is performed on that night is to encourage the children at the table to ask why we perform so many strange acts during that evening instead of proceeding from kiddush to Motzi, breaking bread, directly. Normally, vegetables used to be eaten as a kind of dessert, whereas on this evening we commence with them. We never drink two cups of wine before eating bread, whereas on this evening we make a point of drinking two cups of wine before eating any bread (matzah). As soon as the child sees us pouring the second cup of wine he begins asking questions. The concoction known as …