Some thoughts on matza zo and maror zeh

Just as the zevah pesach should be mentioned, so should the matza. And what significance attaches to matza, that one can see it and point to it and describe something concrete that has to do with the Exodus from Egypt? That is that they were driven out, such that their matzah did not have time to rise, but baked on their backs. Or rather, since they had to leave swiftly, they didn't bake it at home, but baked it on the road, where they did not have access to ovens. (See the Absolut Haggadah for elaboration.)

This is not necessarily the reason we eat matzah -- indeed, matzah was eaten in their homes in Pesach Mitzrayim, but it is the aspect of the redemption that looking at the matzah calls to mind, and so it is that aspect of sippur yitzias mitzrayim that should be discussed.

What prooftext could Rabban Gamliel bring that indeed one must mention matzah (and its significance), or else one did not fulfill his obligation?

It would seem to be the pasuk of Baavur Zeh. In Shemot 13:8:

6. For seven days you shall eat unleavened cakes, and on the seventh day, there is a festival for the Lord.		ו. שִׁבְעַת יָמִים תֹּאכַל מַצֹּת וּבַיּוֹם הַשְּׁבִיעִי חַג לַה':
7. Unleavened cakes shall be eaten during the seven days, and no leaven shall be seen of yours [in your possession], and no leavening shall be seen of yours throughout all of your borders.		ז. מַצּוֹת יֵאָכֵל אֵת שִׁבְעַת הַיָּמִים וְלֹא יֵרָאֶה לְךָ חָמֵץ וְלֹא יֵרָאֶה לְךָ שְׂאֹר בְּכָל גְּבֻלֶךָ:
8. And you shall tell your son on that day, saying, "Because of this, the Lord did [this] for me when I went out of Egypt."		ח. וְהִגַּדְתָּ לְבִנְךָ בַּיּוֹם הַהוּא לֵאמֹר בַּעֲבוּר זֶה עָשָׂה ה לִי בְּצֵאתִי מִמִּצְרָיִם:

Thus, there is a juxtaposition of matza (in pasuk 6 and 7) with sippur yetzias mitzrayim (in 8). And pasuk 8 states Baavur Zeh, "because of this". Because of what? On a peshat level, I might say that the zeh is the implicit [this] above, or that זה functions as conjunctive asher, that is it is because asher Hashem did this for me.

Rashi says:

Because of this: In order that I fulfill His commandments, such as these [commandments of] the Passover sacrifice, matzah, and bitter herbs. — [from Jonathan, Passover Haggadah]

בעבור זה: בעבור שאקיים מצותיו, כגון פסח מצה ומרור הללו:

Thus, "this" refers to the commandments, such as Pesach, Matzah, Maror.

Here is what Ibn Ezra has to say:

בעבור זה -אמר רבי מרינוס: 

פירוש בעבור זה. היה ראוי להיותו הפך זה בעבור שעשה ה' לי. 

והביא רבים כמוהו לדעתו. 

ולפי דעתי: 
אין אחד מהם נכון. כי איך נהפוך דברי אלוהים חיים. וטעם הפסוק הפך מחשבתו. כי אין אנו אוכלים מצוות בעבור זה. רק פירוש בעבור זה, בעבור זאת העבודה שהוא אכילת המצה ולא יאכל חמץ, שהוא תחלת המצוות שצוה לנו השם. עשה לנו השם אותות עד שהוציאנו ממצרים. 
והטעם לא הוציאנו ממצרים רק לעבדו ככתוב: בהוציאך את העם ממצרים תעבדון את האלהים על ההר הזה.
וכתוב: אשר הוצאתי אתכם מארץ מצרים להיות לכם לאלהים.

He cites Rabbenu Yona Ibn Janach that it is reversed. Zeh, this, meaning the sacrifice, or perhaps the matzah and the maror separately of inclusive, is baavur of what Hashem did.

If so, we have the sippur which is prompted by the zeh, that "this [X, Y, Z] is because of the redemption."

Ibn Ezra does not like this explanation and instead says that "the redemption was because of our eventual [X, Y, Z]", just like Rashi.

Regardless, zeh is something you can point to. And there is the derasha we saw earlier in the Haggadah: If bayom hahu, maybe while it was yet day? No, since it says baavur zeh, it is only when the Pesach, Matza, and Maror are sitting before him.

So we need to mention the matzah and a Biblical significance to the matzah, as it relates to the Exodus.

Maror and its pasuk is curious. Of course maror is part of the baavur zeh, since the Pesach was eaten al matzos umerorim.

But there is no explicit pasuk telling why one eats maror. Indeed, some rationalist Rishonim, such as Ibn Caspi, view it as a health injunction, to have vegetables with one's meal. But there is a linguistic link between "they embittered their lives" and maror, and this is good enough. And so the pasuk cited is וימררו את חייהם.

Unless we take ומצות על מרורים יאכלוהו as meaning that one ate the matza, etc., upon, that is because of, the bitternesses.