The Mishnah (Pesachim 35a) excludes the use of tevel (produce that has not been tithed and is therefore forbidden food) for the fulfillment of the mitzvah of matzah on Pesach night. The gemara (35b-36a) justifies this disqualification based on the rule of "ein issur chal al issur" (an existing prohibition is not subject to an additional injunction). Thus, the status of tevel would preclude the further prohibition of chametz that applies on Pesach. Consequently, tevel cannot produce matzah based on the ruled invoked by the gemara that only that which is subject to the issur of chametz may qualify for the mitzvah of matzah.
The Ramban (Pesachim 35b) rejects the mishnah's ruling because he concludes that a more expansive and inclusive issur such as chametz (issur mosif) would apply even to tevel. In his view, tevel matzah would accomplish the mitzvah since tevel could conceivably violate chametz, although one would also violate the injunction against tevel. The Ramban notes an apparent inconsistency in the Rambam's position on this matter. The Rambam (Hil. Chametz 6:7) excludes tevel matzah like the mishnah even though he does not accept the gemara's rationale regarding "ein issur chal al issur"!
In fact, the Rambam projects a different justification for the exclusion of tevel matzah, asserting that any substance that does not warrant a birchat ha-mazon will not qualify for the mitzvah of matzah. The commentators struggle with the source and logic of this principle. Perhaps a better understanding of the objective of sippur yetziat Mitzrayim generally and of the role of matzah specifically may clarify the Rambam's thinking.
It is particularly the Rambam (Sefer ha-Mitzvot, aseh no. 157) who develops the idea that sippur yetziat Mitzrayim transcends relating the detailed events of the exodus and acknowledging their theological and spiritual significance. He articulates that personal hodaah (thanksgiving) is an essential component, as well. This concept is reflected in the gemara's (Pesachim 116a) report that one who comprehends that liberation coupled with self-sufficiency must stimulate personal gratitude and praise is exempt from formulating the mah nishtana passage, as the principles of the passage have already been internalized. Indeed, more than any halachic authority, the Rambam (Hil. Chametz 7: 6) accentuates the need to personalize the experience of the exodus and to express it demonstratively (See Pesachim 116a, and Hil. Chametz 7:6-7, and compare 8:5). The Rambam also intensifies the link between the haggadah experience and the chapter of arami oved avi- mikra bikkurim (See Pesachim 116a, and Hil. Chamtez 7:4), which underscores the theme of personal thanksgiving.
The seder revolves around the four cups of wine, each representing a different motif of redemption and sippur yetziat Mitzrayim. Three of the four cups are linked with themes that have evident significance on this night. The kiddush of the seder (cup 1) is perceived by some halachists as the actual berachah of sippur yetziat Mitzrayim. The second cup focuses on the actual story of the exodus (maggid), culminating with the sections of hallel that are devoted to the events of this night. The fourth cup (birchat ha-shir) completes the hallel by applying, expanding, and universalizing the implications of the exodus experience. Only the third cup-birchat ha-mazon, appears to be generic and routine, disconnected from the specific themes of the night. However, in light of the essential role of personal hodaah, this conclusion should be reassessed. Birchat ha-Mazon is, after all, the quintessential blessing for thanksgiving. According to many authorities, it may be the only Biblically mandated beracha!
The mitzvah of matzah is particularly related to this theme of thanksgiving. The Gaon of Vilna explains that the beginning section of the haggadah, ha lachma anya, establishes matzah as lechem oni (poor bread) as the paradigm for the four categories who are obligated to give thanksgiving (arbaah tzerichin lehodot- Berachot 54). The Gaon explains that the four questions, four sons, four formulations of redemption etc. all reflect the theme that is encapsulated in matzah!
The Maharsha (Pesachim 116a-b) questions why the mitzvah of matzah requires an accompanying formula (R. Gamliel) beyond the routine beracha, why one formulation in the mishnah links it to redemption (al sheim she-nigalu vs. al sheim shelo hispik bezeikam etc.), and why the nation was involved in this mitzvah even before they actually departed from Egypt. He concludes that matzah also constituted a form of korban, like menachot which were made of matzah. It appears that he is referring to the model of korban todah.
Although korbon todah actually contained a component of chametz (Vayikra 7:12-14), it is noteworthy, as the Ramban indicates, that the Torah defines that korban primarily in terms of the matzah loaves, while the chametz is mostly an adjunct to the korban. [See, also, Ramban's remarks 7:14 on the difference between todah and shetai ha-lechem. In light of his insight in 7:13, one might suggest and additional solution...] The Seforno argues that the chametz's function in the todah is to insure that in our euphoria we do not ignore the catalyst to our initial distress and become complacent regarding future challenges to our spiritual and physical wellbeing. It is possible that the mitzvah of matzah on the seder night represents a more pristine form of todah, one which does not allow any chametz, one in which all the ingredients are worthy of the mizbeach. Moreover, the formula of "matchilin be-genai u-mesaiymin be-shevach" in the context of mitzvat sippur yetziat Mitzrayim and matzah guarantees a balanced assessment of the past that helps to secure a proper perspective in the present. The Chatam Sofer (commentary on hagadah) suggests that the first question of the mah nishtana focuses on why chametz could not be eaten as a prelude to the matzah of Pesach just as chametz can be eaten before any korban minchah. The response provided in the section of 'avadim hayinu" conveys the idea that Klal Yisrael emerging from Egypt required a more radical rejection of chametz and an absolute immersion in the symbol of matzah.
We may now return to the innovative and apparently enigmatic formula of the Rambam. The Rambam postulated that one cannot fulfill the mitzvah of matzah with any substance that is disqualified for a birchat ha-mazon. We can now better appreciate that a matzah that does not stimulate the blessing of thanksgiving contravenes the very objective of mitzvat matzah. In this principle, the Rambam succinctly and profoundly formalized the central function of personal and national thanksgiving on this singular evening.